Do words matter?

Do words matter? Does it make a difference what we speak? Often the common opinion seems to undervalue words, and of course finally it is more relevant what a person does, rather what he speaks. For example Jesus explained to the disciples by asking who of the sons did the will of the father: the one who said "yes, I will do the task" but did not, or the one who first rejected to do but finally went out and accomplished the work? Ultimately the deeds are more relevant. But words are often also part of the deeds. God created the universe by speaking words. Jesus healed people by speaking words. And all of us either build up by using constructive words or we tear down by using destructive words.