Eph 4:29&31 Let no corrupt word proceed out of your mouth, but what is good for necessary edification, that it may impart grace to the hearers. 31 Let all bitterness, wrath, anger, clamor, and evil speaking be put away from you, with all malice.
Unkind words spoken to a person can cause great hurt and we are warned against the use of the tongue many times in scripture. However, our words do not have a special power of their own. If we could actually speak things into existence we would see all kinds of crazy things going on all over the world.
This belief is a twist on Romans 4:16-17, taking it out of its context with the emphasis solely on the latter part of verse seventeen. But read in its entirety –
16 Therefore, the promise comes by faith, so that it may be by grace and may be guaranteed to all Abraham’s offspring—not only to those who are of the law but also to those who are of the faith of Abraham. He is the father of us all. 17 As it is written: “I have made you a father of many nations.” He is our father in the sight of God, in whom he believed—the God who gives life to the dead and calls things that are not as though they were.
Power belongs to God and to Him alone and that is what this verse is getting at. It is God who calls these things, not people.
We are told to not curse a person, or to speak badly of someone because to do so simply is not Christ-like. Idle words and babblings are worthless to the hearers and can cause pain to others. Effects from ill-spoken words take root in the mind because the receiving person, for whatever reason, chooses to believe them. When a believer experiences such things the focus should be on Christ and what the Lord says is true.
Romans 12:2 And do not be conformed to this world, but be transformed by the renewing of your mind, that you may prove what is that good, and acceptable and perfect will of God.
Our words don’t have supernatural power of cause and effect, nor can they “speak things into existence”, nor do they have the power to create. Regardless of all the support that we can and should “declare!” or “decree!” when we pray, the Word of God simply does not tell us so.