“For to which of the angels did He ever say, You are My Son; today I have become Your Father, or again, I will be His Father, and He will be My Son? (Hebrews 1:5 HCSB).
If Jesus is God, then how could God “become” His Father? Theologians and Biblical commentators have addressed that question in several different ways…
“The word ‘TODAY’ indicates that God’s Son was born in a point of time. He was always God, but He demonstrated His role as Son in space and time at His incarnation and was affirmed as such by His resurrection (Ro 1:4).” (1)
“Jesus has always been deity (cf. John 1:1-18). Therefore, [today I have begotten you] cannot refer to the essence of His nature, but to His manifestation in time (the incarnation).” (2)
“The Son is eternally begotten by the Father. He is equal to the Father, but he is called a Son, and the Bible speaks of his being begotten. God exists in eternity, so there was never a time when the Son did not exist. Begetting is not an event in time; it simply describes the relationship between Father and Son. The Son is eternally mature and equal to the Father and also eternally begotten by the Father. This is a mystery because we cannot imagine a timeless state.” (3)
“Jesus was uniquely God’s son by nature—meaning that he has the very nature of God. It is significant that when Jesus claimed to be the Son of God, his Jewish contemporaries understood him to be claiming deity in an unqualified sense and sought to stone him: ‘We have a law, and according to that law he [Jesus] ought to die, because he made himself out to be the Son of God’ (John 19:7 NASB, insert added). They thought Jesus was committing blasphemy because he was claiming deity for himself.
Many evangelicals believe that Christ’s sonship is an eternal sonship. Evidence for Christ’s eternal sonship is found in the fact that he is represented as already the Son of God before his human birth in Bethlehem (John 3:16– 17; cf. Prov. 30:4). Hebrews 1:2 says God created the universe through his ‘Son’—implying that Christ was the Son of God prior to the Creation. Moreover, Christ as the Son is explicitly said to have existed ‘before all things’ (Col. 1:17; compare with vv. 13–14). As well, Jesus, speaking as the Son of God (John 8:54–56), asserts his eternal preexistence before Abraham (v. 58). Seen in this light, Christ’s identity as the Son of God does not connote inferiority or subordination either of essence or position.” (4)
(1) MacArthur, J. F., Jr. (2006). The MacArthur study Bible: New American Standard Bible. (Heb 1:5). Nashville, TN: Thomas Nelson Publishers.
(2) Dr. Bob Utley, Hebrews 1 [1:5] Copyright © 2014 Bible Lessons International http://www.freebiblecommentary.org/new_testament_studies/VOL10/VOL10_01.html
(3) Sproul, R. C. (1994). Before the face of God: Book 4: A daily guide for living from Ephesians, Hebrews, and James (electronic ed.). Grand Rapids: Baker Book House; Ligonier Ministries. [Page 30]
(4) Norman L. Giesler and Ron Rhodes, When Cultists Ask A Popular Handbook on Cultic Misinterpretations [note on John 3:16] Baker Books, 1997