In the book of Joshua, God speaks to Joshua and tells him, “No man will be able to stand before you all the days of your life. Just as I have been with Moses, I will be with you; I will not fail you or forsake you.”
Christian exegesis can take the Old Testament and apply it to believers in the new covenant. That is what the author of Hebrews does. He takes the verse from Joshua and says: “Let your character be free from the love of money, being content with what you have; for He Himself has said, “I will never desert you, nor will I ever forsake you…” The promise to Joshua is now a promise to all of us with (surprisingly) financial implications.