If anyone else was saying this we would probably just dismiss this as some Dangerous New Age Philopsophy. But it is our Lord and Savior Jesus Christ, who demonstrated the truth of it all through His ministry on earth – so we had better listen.
Jesus does not even say that this applies to believers in Him only. He says ‘Whoever …’ It is required however that one truly believes 'in his heart' and does not doubt that those things he says will be done. We need to consider then what believing in one's heart means, because this is one of the essential ingredients for effective power ministry.
The other important aspect here is the power of 'words'. Its interesting that Jesus uses the word 'says' three times in this verse. It really adds emphasis if you think about it. 'Whoever say … those things he says will be done … he will have whatever he says.'
There is a powerful truth here. The words we speak have a real existence. They are "things". I'm told that the word for "word" and the word for "thing" is the same in both the Hebrew and Greek languages.
If we want to cast out demons or diseases, we can speak to them and command them to move. If we do not doubt in our hearts, it will happen. Doubts may arise for any number of possible reasons:
1. We are not accustomed to believing that God will do great things, we haven't seen it before, therefore we don't believe because we don't yet know God in that way.
2. We assume that if it was really so some trusted religious figure in our life would be demonstrating it already.
3. We may have unconfessed, undealt with sin in our lives producing guilt, uncertainty or lack of confidence.
4. There is someone out there who has hurt us and we have not trult forgiven them. (See Mark 11:26)
5. We really aren't sure if it is God's will and we think it may not be, therefore it won't happen.
6. We ourselves may not have invested time in meditating on the truths confirming the importance of what we are saying and believing for.
7. We are bound by a cynical, skeptical, materialistic, rationalistic mindset.
8. We may not have the assurance from God that this is the right time to speak.
However, if none of these things apply to the case, and we really DO believe in our hearts, we need to SPEAK OUT AND COMMAND WHAT WE DESIRE to happen. Tell the disease to go, the bones to move into place, the organs to be healed or made new. Do it, say it, don't doubt, and miracles will be the result.
I've seen that this works. The key of course is in preparing your heart before the Lord so that you CAN believe and not doubt. The other key is to keep speaking the things you desire, especially when you know from the Scriptures that those desires are God's desires also.