Hebrews 13:8 - Jesus Christ is the same yesterday, today, and forever.
According to some, this scripture proves that Jesus always has been, is, and always will be, that he has never changed from all eternity past, and never will change for eternity future. Usually, this scripture is presented in connection with Malachi 3:6, where Yahweh states: "For I [am] Jehovah, I have not changed, And ye, the sons of Jacob, Ye have not been consumed." (Young's Literal Translation) Yahweh declares that, although for a time Israel is left in fiery trials, yet he has not changed his mind concerning Israel so that Israel should be consumed by those fiery trials, but rather, as Paul says, "the gifts and the calling of God are irrevocable." (Romans 11:29) Thus Paul wrote: "and so all Israel will be saved. Even as it is written, "There will come out of Zion the Deliverer, And he will turn away ungodliness from Jacob. This is my covenant to them, When I will take away their sins." -- Romans 11:26,27.
Of course, Hebrews 13:8 is speaking of Jesus, not Yahweh. Yes, by means of his faithfulness to Yahweh has indeed proven himself the same yesterday, today, and forever. Jesus never disobeyed his God and Father, and has proven through all of his sufferings that he is incorruptible. It by his obedience that brought life and incorruption to light. (2 Timothy 1:10)
The writer to the Hebrews, in context, writes about imitating the faith of those who take the lead amongst the believers, and he warns against being carried away with false teachings. In between this he states "Jesus Christ is the same yesterday, today and forever." Evidently this has some connection to the context. The writer did not just suddenly change the subject so to announce, as some would have it, that Jesus exists, always existed and will always exist.
In actuality, "yesterday" does not mean all eternity past, nor did the writer say anything about Jesus never having a beginning. This idea has to be added to, and read into, what was stated.
As regarding an example of a leader and a faith to imitate, however, Jesus never wavered in his faithfulness to his God and Father. Jesus' faithfulness was mentioned earlier in Hebrews 2:17 and 3:2.
Nor does Hebrews 13:8 say anything about Jesus' always have been the same "substance," as some seem to read into the words. There is certainly absolutely nothing in the words that says that Jesus is the God of Abraham, Isaac and Jacob, He who is from everlasting to everlasting. Such ideas have to assumed outside of what the scripture actually says and then added to and read into the scripture.