God expects us to keep our promises. It's in the Bible, Numbers 30:1-2, NIV. "This is what the Lord commands; When a man makes a vow to the Lord or takes an oath to obligate himself by a pledge, he must not break his word but must do everything he said."
Don't delay keeping your promises to God. It's in the Bible, Ecclesiastes 5:4-5, TLB. "So when you talk to God and vow to Him that you will do something, don't delay in doing it, for God has no pleasure in fools. Keep your promise to Him. It is far better not to say you'll do something than to say you will and then not do it."
God always keeps His promises. It's in the Bible, II Corinthians 1:19-20, TLB. "[Jesus Christ] isn't one to say yes' when he means no.' He always does exactly what He says. He carries out and fulfills all of God's promises, no matter how many of them there are; and we have told everyone how faithful He is, giving glory to His name."
God never takes back or changes his promises. It's in the Bible, Psalm 89:34, TLB. "No, I will not break my covenant; I will not take back one word of what I said."
None of God's promises ever fail. It's in the Bible, Joshua 23:14, NIV. "You know with all your heart and soul that not one of all the good promises the Lord your God gave you has failed. Every promise has been fulfilled; not one has failed."