… there is nothing more certain than God’s promise. Nothing! He intends for us to base our life, our future, our hope, our eternal destiny upon His promise (see 2 Pet. 1:3-11, noting the foundational “precious and very great promises”).
Basing everything on a person’s promise is risky. Iffy proposition. On God’s promise, doing such is solid, since he has never failed to keep it.
Some suggest that God, on the day of judgment, might change his terms of salvation. Don’t believe it! What he says in his Word he will do.