Malachi 3:6, "For
I am the LORD, I change not;
therefore ye sons of Jacob are
However, all three of those things are not applicable to God. He cannot lie, He cannot deny Himself, and He is without end and not subject to death. Therefore, God will not fail you, because there are some things that He CANNOT DO. He says that He is the LORD. That plainly declares that there is no being in the universe that can challenge His authority and word. He also says that He does not change. This means that what is true today is true tomorrow.
We live in a world where people seem to think that the truth changes from day to day. The truth is the truth no matter what day it is or how much time passes. The truth is also the truth whether someone believes it or not. Therefore, people can deny what God has said or promised from now until they press the dying pillow, but it will not negate the fact that the Lord has promised these things and they do not change.
Finally, the Lord says that His immutability is what keeps us from being consumed, annihilated, and in shame and contempt. There is no power that can reach the Lord's children because we are in Christ's hand and He is in the Father's hand. No man can pluck us from that position and therefore, we shall never perish. Oh how comforting it is to know that He will never leave us nor forsake us!