Consider the following. If we could travel at a septuagintacentillion (10513) times the speed of light in any one direction, would we ever find the end of the universe, like perhaps a wall with a sign saying this is the end? And if so, what would be on the other side of that wall? And what existed before God created all things through His Son? Was it nothing? And how long did nothing exist for if that was the case? It would have to be forever! And what about God, when did He begin to exist and who created Him? The answer is that there was never a time He did not exist and hence could never have been created. He is God and has always been and so is without beginning! And what about the Son of God who was born of the same substance of God? The same applies.
Since Christ is the same substance of His Father, then everything He consists of had no beginning. So His divinity had no beginning, His makeup; His nature had no beginning as it all came from the Father. So in principle, everything Christ is had no beginning. If you trace Christ back you will have to go through the Father and you will never get to a beginning. But His personality as the Son of God began when He was brought forth by His Father. So in effect it was only the personality of Christ that had a beginning. These are the mysteries of God and things our mind cannot possibly comprehend.
“The Lord Jesus Christ, the only begotten Son of the Father, is truly God in infinity, BUT NOT IN PERSONALITY.” — (E.G. White, MS116, December 19, 1905)
Waggoner explains in words that are easier to understand making what Ellen White said above easier to comprehend.
“Jesus is the only begotten Son of God. He was begotten, not created. He is of the substance of the Father, so that in his very nature he is God; and since this is so “it pleased the Father that in him should all fullness dwell.” Col. 1:19 ... While both are of the same nature, the Father is first in point of time. He is also greater in that he had no beginning, WHILE CHRIST'S PERSONALITY HAD A BEGINNING.” — (E.J. Waggoner, ST, April 8, 1889)
“Angels of God looked with amazement upon Christ, who took upon Himself the form of man and humbly united His divinity with humanity in order that He might minister to fallen man. ... And although we may try to reason in regard to our Creator, HOW LONG HE [Christ] HAS HAD EXISTENCE, where evil first entered into our world, and all these things, we may reason about them until we fall down faint and exhausted with the research when there is yet an infinity beyond.” — (Ellen G. White, 7BC 919.5)
Below Waggoner states that it was so far back in time that it was practically without beginning.
“As to when He was begotten, it is not for us to inquire, nor could our minds grasp it if we were told. The prophet Micah tells us all that we can know about it in these words, “But thou, Bethlehem Ephratah, though thou be little among the thousands of Judah, yet out of thee shall He come forth unto Me that is to be ruler in Israel; whose goings forth have been from of old, from the days of eternity.” Micah 5:2, margin. THERE WAS A TIME WHEN CHRIST PROCEEDED FORTH AND CAME FROM GOD, FROM THE BOSOM OF THE FATHER (John 8:42; 1:18), but that time was so far back in the days of eternity that to finite comprehension it is practically without beginning.” — (E.J. Waggoner CAHR, pp. 21, 22)