Doctrine of the Eternal Sonship of Christ

Question: Was Jesus Christ "eternally" the Son of God before the foundation of the world or did He "become" the Son at His incarnation?

Briefly, the doctrine of the Eternal Sonship of Christ is this:

Quote:
The doctrine of eternal Sonship declares that the Second Person of the triune Godhead has eternally existed as the Son. His Sonship had no beginning. There was never a time when He was not the Son of God. There has always been a Father/Son relationship in the Godhead. Sonship is not merely a title or role or function that Christ assumed at some point in history, but it involves the essential identity of the Second Person of the Godhead. He is and has always been the true, proper, actual Son of God.

Those who deny eternal Sonship teach that Christ became the Son at some point in history—at His incarnation, at His baptism, at His resurrection or at His exaltation. Most who deny eternal Sonship say that He became the Son at His birth (at the incarnation), and that prior to Bethlehem He was not the Son of God. They do not deny His deity or His eternality, but they deny His eternal Sonship. Some teach that the term “Son of God” means “subservient to God, less than God, inferior to God.” They believe that Christ's Sonship is external, extrinsic, and extraneous to the real, true, proper, and essential essence of who Jesus Christ really is. Thus they teach that Sonship was merely a role or a title or a function that Christ assumed at the incarnation. They also teach that the Father became the Father at the time of the incarnation.

Those who teach this view would include Ralph Wardlaw, Adam Clarke, Albert Barnes, Jimmy Swaggart, Finis J. Dake (Dake's Annotated Reference Bible), Walter Martin (author of Kingdom of the Cults). Popular Bible teacher John MacArthur, Jr. for many years denied the doctrine of the eternal Sonship of Christ, but he has changed his position and now embraces this doctrine.
(from Middletown Bible Church.org)

The Scripture says in Hebrews 13:8:

Jesus Christ the same yesterday, and to day, and for ever. (Hebrews 13:8)

I think just that one verse pretty much speaks for the eternal Sonship of Christ.

Any thoughts?

Source: http://seekgod.ca/forum/showthread.php?tid=246