The Greek word translated "only begotten," μονογενής (monogenēs), also appears in relation to three other characters in the Bible. The widow from Nain, a tiny Galilean village, was on her way to bury her "only" son when she encountered Jesus (Lk. 7:12). Jairus, a ruler of a synagogue, asked the Lord to help his "one only" daughter (Lk. 8:42). The father of the demon possessed asked Jesus to help "mine only" son (Lk. 9:38).
One might believe that due to the Science of Genetics, the translators looked at the Greek word, and saw it to mean Jesus had only one human parent. However, not only could the writers of the Bible not have meant this, neither could the translators of the King James Bible. The first person to publish scientific findings on genetic reproduction, was Gregor Mendel, and he didn't publish his results until 1865, two hundred and fifty-four years after the KJV was translated. And, due to the fact that the same translation was used to describe Isaac's relationship to Abraham, the words, "only begotten" should not be seen as a Bible mystery concerning the Virgin Birth of Christ.
The Good News is, God does have millions of children. Believers in Christ have been adopted by God; we are His sons and daughters. The Apostle Paul wrote: "For as many as are led by the Spirit of God, they are the (children) of God. For ye have not received the Spirit of bondage again to fear; but ye have received the Spirit of adoption, whereby we cry, Abba, Father. The Spirit itself beareth witness with our spirit, that we are the children of God" (Rom. 8:14-16).
We may not be "begotten," but we definitely are "beloved!"