Tradução em português aqui.
So in Christ Jesus you are all children of God through faith, for all of you who were baptized into Christ have clothed yourselves with Christ. There is neither Jew nor Gentile, neither slave nor free, nor is there male and female, for you are all one in Christ Jesus. Galatians 3:26-28 (NIV 2011)
Paul wanted equality for all Christians and he wrote about this in his letters. In some verses, equality is implied, as in Galatians 3:26-28. In other verses, the concept of equality is more clearly stated.
The Greek word for “equality” is isotēs. Because fairness is the result of equality, isotēs can also have the meaning of “fairness” and “equity”. It can even mean “sameness”. Paul used the word isotēs once in Colossians 4:1 and twice in 2 Corinthians 8:13-14. (The NASB translates isotēs as “fairness” in Col. 4:1, but “equality” in the 2 Cor. 8:13-14.)
Equality between Slaves and Masters
I was surprised, and pleased, to see isotēs used in the context of slaves and masters in Colossians 4:1. The 1881 Revised Version of this verse reads: “Masters render to your servants what is just and equal; knowing that ye also have a Master in heaven.”
Paul wanted the Christian masters to treat their slaves fairly and with equality. After all, the Christian masters knew what it was like to be a bond-slave under the authority of their heavenly Master. They knew that God was both a merciful Master and a Judge, and that they were answerable to him.
A few verses later, in Colossians 4:9, Paul speaks warmly about Onesimus, a slave whom Paul was sending back to his master. Paul describes Onesimus as “a faithful and beloved brother who is one of you.” That is, Onesimus was to be welcomed and accepted as a fellow and equal member of the Christian community at Colossae.
Paul also wrote a letter to Philemon, the master of Onesimus, asking him to welcome Onesimus back, “no longer as a slave, but more than a slave, a beloved brother” (Philem. 1:15-16; cf, 1 Tim. 6:2). Paul added, “If you [Philemon] regard me as a partner, accept him as you would me” (Philem. 1:17). Paul wanted Philemon to no longer regard Onesimus as a slave, but regard him he would the apostle Paul!
Why were Paul’s instructions for justice and equality, even for genuine brotherly love towards slaves—particularly Christian slaves—not apparent to Christians a few hundred years ago? 
Equality between Poor and Rich
Paul used the word isotēs in 2 Corinthians 8:13 & 14 in the context of economic equality.
. . . the gift is acceptable according to what one has, not according to what one does not have. Our desire is not that others might be relieved while you are hard pressed, but that there might be equality. At the present time your plenty will supply what they need, so that in turn their plenty will supply what you need. The goal is equality . . . 2 Corinthians 8:12b-14 (NIV 2011)
Paul did not want some Christians to have plenty while others were experiencing financial hardship, perhaps even destitution. Paul wanted financial equity among all believers.
The verses in 2 Corinthians 8 have made a strong impression on me. There is nothing close to financial equality and fairness in the world, or among Christians. Many Christians are ridiculously wealthy while many, many more live in wretched poverty. Yet God wants equality. (See also John the Baptist’s words in Luke 3:11.)
This is a challenge for all of us in Western nations. Are you and I—as individuals, families, and churches—willing to share our wealth with our brothers and sisters who live in, sometimes, miserable conditions in poorer nations?
The reasons why we are reluctant to share our wealth are the same reasons why slaves were often not treated as the equal of their masters or given their freedom: Greed and pride. Greed and pride prevent us from relinquishing or diminishing our level of comfort, status, or power. Another reason is our lack of faith. Most of us do not trust that God will provide for our families and churches if we give our money sacrificially. Yet God wants people who are in advantaged situations to help those in disadvantaged situations.
Equality between Women and Men
Another area of inequality among humanity is the continuing inequality between women and men. Many Christians insist that women and men are essentially equal. However, because of the interpretation of a few Bible verses, most Christians still put restrictions on what women can do and can be. And so, women (as individuals and as a group) are not treated as the equal of men. In some cultures, women are treated especially badly and have very few basic human rights and freedoms.
I have heard people (including women) say that women should not “stand up” for equal rights and equal opportunities, and they cite Jesus’ humility and sacrifice as an example. In a way, I agree. While I hope to promote equality for all people, men and women, I have no desire to demand equality for myself.
Jesus did not “stand up” for his rights. He willingly relinquished his divine privileges and humbled himself for the sake of the church. However, Jesus could relinquish his divine rights because he had them in the first place. Jesus truly was, and is, equal with God.
In too many cases, all over the globe and in the church, women are simply denied equality. They do not have rights that they can voluntarily relinquish if they choose to do so. It is unjust, and illogical, to tell a woman to surrender rights that she does not actually have. Moreover, it is the people in advantaged situations (not the disadvantaged people) who are to share or give up certain benefits and privileges if we are to see equality.
Instead of asking women to give up the right or expectation of equal opportunities and freedoms, it is preferable if men, who are generally in an advantaged, privileged position, could see women as true equals, treat women as true equals, and actively encourage gifted women in worthwhile pursuits, including ministry pursuits.
Paul valued his female colleagues and encouraged women in ministry. The last chapter of his letter to the Romans contains warm commendations, and sincere salutations, to several women ministers. Here, and in his other letters, Paul used the same titles and descriptions for male ministers as for female ministers, titles such as apostle, minister, and co-worker. Paul regarded and treated all believers as equal, as brothers and sisters.
Equality in the Church
The very early church made attempts at, and occasionally experienced, equality. Christians gave sacrificially so that no one was in need (Acts 4:32-35). Slaves were very much a part of church communities. Some slaves, both men and women, were even ministers. Economic, social, racial, and gender barriers were broken down as Spirit-empowered ministry dealt with issues of greed, pride, and bigotry, and fostered equality.
Perhaps promoting equality is a spiritual gift. It seems that Paul had this gift. Paul used his influence to help those who were disadvantaged, people such as slaves and those experiencing poverty and injustice. Equality was Paul’s goal (2 Cor. 8:14, NIV 2011).
Christians in advantageous situations and influential positions today have an obligation to help those who are disadvantaged so that we can progress towards the Kingdom ideal of equality for all people.
Do you have a spiritual ministry gift of promoting equality, fairness, and justice? Is equality your goal? Who can you help?
 The prefix iso, which is used in some scientific and technical terms, comes from the Greek and means “equal”. Some terms which use the prefix iso are:
- Isobars, lines on weather maps that join places that are experiencing the same/equal barometric (atmospheric) pressure;
- Isotopes, elements with the same/equal number of protons but different numbers of neutrons in their nuclei;
- Isosceles, an isosceles triangle has two equal sides.
 BDAG gives as the definition of isotēs: “(1) state of matters being held in proper balance, equality . . . (2) state of being fair . . .” A Greek-English Lexicon of the New Testament and Other Early Christian Literature, 3rd Edition, by Walter Bauer, revised and edited by F.W Danker (University of Chicago Press, 2000), 481.
 My translation of Colossians 4:1a: “Masters, grant justice and equality to your slaves . . .”
 We have ample evidence that slaves, including female slaves, were very much part of the early church communities. Some slaves were even ministers. In his letter to the Roman emperor Trajan, in around 111-113AD, Pliny (governor of the province of Pontus and Bithynia in Asia Minor) wrote that he had tortured and interrogated two Christian slave women. He writes that these women were called “ministers” (Latin: ministrae). (Pliny the Younger, Epistle to Trajan, 10:96) [More on this here.]
Slaves who became church leaders exemplify the equal standing of slaves in the church. Within a half century of Paul’s writing the letter of Philemon, Ign[atius in I]Eph. 1:3 “speaks highly of “Onesimus, a man of inexpressible love and your bishop.” Onesimus was a common slave’s name and so exemplifies this, whether or not this bishop of Ephesus was formerly Philemon’s slave. The Muratorian Canon, lines 73-77 identifies Pius I, Bishop of Rome, either as a slave or the brother of the slave Hermas, the author of the Shepherd. Similarly, Hippolytus, Haer. 9.11f. says that Callixtus [or, Callistus], bishop of Rome AD 217-222, was an ex-slave.
Philip B. Payne, Paul Applies Maximum Social Pressure for Philemon to Free Onesimus, 2009, p.3.
 Paul’s letter to the Colossians and his letter to Philemon were delivered by Onesimus, possibly the same Onesimus who later became bishop of the church at Ephesus. (See note above.)
 In Paul’s short letter to Philemon, Paul sets the tone of his letter by mentioning affection/compassion (splagchna) three times (Philem. 1:7, 12, 20). Paul wanted Philemon’s actions towards Onesimus to be motivated by love and compassion rather than a sense of duty or compulsion (Philem. 1:8, 14b). Paul wanted Philemon to regard Onesimus with affection and treat him, no longer as a slave, but as a beloved brother, both in the flesh (i.e. as a real brother) and in the Lord (i.e. as a Christian brother)! (Philem. 1:16).
While a common assumption is that Onesimus was a runaway slave, the text does not support this assumption. Philemon may have sent Onesimus to minister to Paul while Paul was imprisoned.
 It is important to note that the system of slavery in the New Testament world was very different from the slavery in America during the 17th-19th centuries.
 Paul uses a cognate of isotēs in Philippians 2:6. Here Paul wrote that Jesus did not grasp at being equal (isa, from isos) with God, the implication being that Jesus was/is equal with God. Jesus as a member of the Trinity is equal with God, yet he chose to temporarily lay aside his divine privileges in order to fulfil his earthly mission. Jesus exemplified humility and submission as he himself took on human form, even the form of a slave, for our sake (Phil. 2:7). In John 5:18, Jesus was accused of making himself equal (ison, from isos) with God.
 Similarly, it would be unfair to tell a slave or a poor person not to stand up against injustice, oppression and poverty, and then do nothing to help them.
 Paul encouraged both men and women in ministry, except for those who were teaching heresy (cf. 1 Timothy 2:12).
 The women in Romans 16 are: Phoebe (Rom. 16:1-2), Priscilla (Rom. 16:3-5), Mary (Rom. 16:6), Junia (Rom. 16:7), Tryphena and Tryphosa (Rom. 16:12) Persis (Rom. 16:12), Rufus’ mother (Rom. 16:13), Julia (Rom. 16:15), and Nereus’ sister (Rom. 16:15). [My article on Paul’s Personal Greetings to Women Ministers here.]
 Junia is called an apostle. Phoebe is called a minister (diakonos). As stated many times on the site, Paul only used the word diakonos for a minister. Paul referred to several men and women as his co-workers in the gospel including Priscilla and Aquila (Rom. 16:6); Urbanus (Rom. 16:9); Timothy (Rom. 16:21); Titus (2 Cor. 8:23); Epaphroditus (Phil. 2:25) Euodia, Syntyche and Clement (Phil. 4:3); Aristarchus, Mark and Justus (Col. 4:10-11); Philemon (Philem. 1:1); Mark, Aristarchus, Demas and Luke (Philem. 1:24).
The Early Church and Slavery
The Holy Spirit and Equality
Equality and Unity in Ministry: 1 Corinthians 12
A Thrill of Hope: Jesus’ First and Second Advents
Galatians 3:28 – Our Identity in Christ and in the Church
Paul and Women, in a Nutshell
Are Women Pastors Mentioned in the New Testament?
Race and Gender Discrimination in the Church
Gender Division Divide the Church
Peace on Earth