Your word is important, that is if you want people to believe you. God gives us His word chocked full of promises that we can believe. There should be no doubt when comes to believing that he will do what He said He would do.
How do I know? Jesus predicted his death and his resurrection. Jesus died on the cross for all humanity. So the reality of his resurrection brings truth and promise that He is a man of his word. Believe it.
God's promises are true. God has given us His son Jesus to prove it!