God keeps His promises.  We easily forget what they are.  Remembering the promises helps our unbelief.

Joshua reminds the people of promises kept.  God had worked miracles to bring the people out of Egypt.  Moses led them through the wilderness for forty years, and Joshua took over leadership as they moved into the Promised Land.  After some years of effort (obeying God is WORK!), Joshua called the people together to remind them where they had been.

“Thus the Lord gave to Israel all the land that he swore to give to their fathers. And they took possession of it, and they settled there. And the Lord gave them rest on every side just as he had sworn to their fathers. Not one of all their enemies had withstood them, for the Lord had given all their enemies into their hands. Not one word of all the good promises that the Lord had made to the house of Israel had failed; all came to pass.”

Joshua 21.43-45 (ESV)