John 3:18 He that believeth on him is not condemned: but he that believeth not is condemned already, because he hath not believed in the name of the only begotten Son of God.
That translation “Only Begotten” originated with the early church fathers and it entered into the early English translations of the Bible because of the heavy influence of the Latin Vulgate, the Roman Catholic Bible. The perspective that Christ was born from The Father came from Origen, one of the early scholars of Christianity. He held a number of unscriptural views, such as God the Father alone is God in the highest sense.
He also held that the Christ of the Bible is God, but only in the secondary sense, since according to Origen’s interpretation, He was a derivative of God, and not absolutely God. So here it is, directly from the horses’ mouth of the Vulgate, or Roman Catholic Bible: "Et Verbum caro factum est, et habitavit in nobis: et vidimus gloriam ejus, gloriam quasi unigeniti a Patre, plenum gratiae et veritatis."
English Translation "And the Word was made flesh, and dwelt among us, (and we saw his glory, the glory as it were of the only begotten of the Father,) full of grace and truth. The concept of Jesus Christ being begotten at some distant point in eternity, is not only foreign to the Bible, but it is just another attempt by the prince of darkness to interfere with the divinity of Christ.
Acts 20: 29 For I know this, that after my departing shall grievous wolves enter in among you, not sparing the flock.
May God add His blessing to the study of His word. “Good night” and God bless!