For God so loved the world, that he gave his only begotten Son …” (John 3:16 KJV)
Arguably, one of the most critical words in Christology, the study of the person and work of Christ, is the Greek word monogenēs. In the past, this adjective has been translated into English as “only begotten.”
The connotations of “only begotten” are slightly ambiguous because “begotten” is no longer part of everyday English and is unfamiliar to modern readers. Furthermore, “begotten,” as in, “brought into existence by means of procreation,” may not be the primary sense intended in John 3:16.
The NIV translates monogenēs meaningfully as “one and only.” John 3:16 in the NIV reads “For God so loved the world that he sent his one and only Son …” The CEB, NLT, CSB, and the ESV likewise have “one and only Son,” or simply “only Son.”
The word monogenēs is used only a few times in the New Testament. Luke and the author of Hebrews use this word about certain people always to emphasise that the person was an only or unique child. The word is not used to emphasise, or refer to, the “begetting” of these children. See Luke 7:12 (the Widow of Nain’s son); Luke 8:42 (Jairus’ daughter); Luke 9:38 (a boy tormented by an evil spirit); Hebrews 11:17 (Isaac).
Monogenēs also occurs a few times in the Septuagint, the Greek version of the Old Testament. In Judges 11:34 it is used for Jephthah’s daughter, an only child. It is used three times in the Psalms, apparently with the senses of “only” and “alone”: “only life” in Psa. 22:20 (LXX 21:21), “alone” in Psa. 25:16 (LXX 24:16), and “only life” in Psa. 35:17 (LXX 34:17). And it occurs in Tobit 3:15 which says, “… I am my father’s only child; he has no other child to be his heir …”
John is the only New Testament author to use monogenēs to describe Jesus. (See John 1:14 & 18, 3:16 & 18, and 1 John 4:9.) He used the word to highlight the unique relationship between God the Father and Jesus Christ. Like the other New Testament authors, John may not have used the word to refer to “begetting” (generation by procreation).
Monogenēs is made from two Greek words. Monos means “alone, only, sole.” Genos has a range of meanings: “offspring, family, relation, lineage, race, kind, species,” etc. However, etymology does not determine a word’s meaning; the way a word is used is what counts. Accordingly, the Greek-English lexicon BDAG define monogenēs as something “that is the only example of its category.” Put more simply, monogenēs means “one of a kind.”
It seems the real implication of this word is that Jesus Christ is God’s “one and only, unique” Son. As such, Jesus shares divinity with the Father in a unique way (Col. 2:9 cf. Heb. 1:3).
 Michael S. Heiser writes,
[Monogenēs] doesn’t mean “only begotten” in some sort of “birthing” sense. The confusion extends from an old misunderstanding of the root of the Greek word. For years monogenes was thought to have derived from two Greek terms mono (“only”) and gennaō (“to beget, bear”). Greek scholars later discovered that the second part of the word monogenes does not come from the Greek verb gennao but rather from the noun genos (“class” or “kind”). The term literally means “one of a kind” or “unique” without connotation of created origin.
Heiser, The Unseen Realm: Rediscovering the Supernatural Worldview of the Bible (Bellingham WA: Lexham Press, 2015) (Google Books)
 According to the Old and New Testaments, as well as Jewish and Christian tradition, Isaac was regarded as Abraham’s only child even though Ishmael has been physically begotten of Abraham before Isaac was born. When Isaac was a grown man, Abraham had even more children with his wife Keturah, including six sons (Gen. 25:1-2). Isaac was Abraham’s uniquely beloved son (Gen. 22:2), the son of a covenant with God (Gen. 17:18-21), and Abraham’s sole heir (Gen. 25:5-6).
 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, 2000. (Known as BDAG for short; an acronym of the four authors who have worked on it: Bauer, Danker, Arndt, and Gingrich.)
 Amazingly, when we become followers of Jesus we too can share in his glorious inheritance as adopted sons and daughters (Rom. 8:14-17; Eph. 1:5).
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