Only Begotten - Vine's Expository Dictionary of New Testament Words
Only Begotten[ 1,,G3439, monogenes ]
is used five times, all in the writings of the Apostle John, of Christ as the Son of God; it is translated only begotten" in Hebrews 11:17 of the relationship of Isaac to Abraham.
With reference to Christ, the phrase "the only begotten from the Father," John 1:14, RV (See also the marg.), indicates that as the Son of God He was the sole representative of the Being and character of the One who sent Him. In the original the definite article is omitted both before "only begotten" and before "Father," and its absence in each case serves to lay stress upon the characteristics referred to in the terms used. The Apostle's object is to demonstrate what sort of glory it was that he and his fellow Apostles had seen. That he is not merely making a comparison with earthly relationships is indicated by para, "from." The glory was that of a unique relationship and the word "begotten" does not imply a beginning of His Sonship. It suggests relationship indeed, but must be distinguished from generation as applied to man.
We can only rightly understand the term "the only begotten" when used of the Son, in the sense of unoriginated relationship. "The begetting is not an event of time, however remote, but a fact irrespective of time. The Christ did not become, but necessarily and eternally is the Son. He, a Person, possesses every attribute of pure Godhood. This necessitates eternity, absolute being; in this respect He is not 'after' the Father" (Moule). The expression also suggests the thought of the deepest affection, as in the case of the OT word yachid, variously rendered, "only one," Genesis 22:2, Genesis 22:12; "only son," Jeremiah 6:26; Amos 8:10; Zechariah 12:10; "only beloved," Proverbs 4:3, and "darling," Psalms 22:20; Psalms 35:17.
In John 1:18 the clause "the only begotten son, which is in the bosom of the Father," expresses both His eternal union with the Father in the Godhead and the ineffable intimacy and love between them, the Son sharing all the Father's counsels and enjoying all His affections. Another reading is monogenes Theos, "God only-begotten." In John 3:16 the statement, "God so loved the world that He gave His only begotten son," must not be taken to mean that Christ became the only begotten son by incarnation. The value and the greatness of the gift lay in the Sonship of Him who was given. His Sonship was not the effect of His being given. In John 3:18 the phrase "the name of the only begotten son of God" lays stress upon the full revelation of God's character and will, His love and grace, as conveyed in the name of One who, being in a unique relationship to Him, was provided by Him as the object of faith. In 1 John 4:9 the statement "God hath sent His only begotten son into the world" does not mean that God sent out into the world one who at His birth in Bethlehem had become His Son. Cp. the parallel statement, "God sent forth the Spirit of His Son," Galatians 4:6, RV, which could not mean that God sent forth One who became His Spirit when He sent Him.