Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours. Mark 11:24 (NIV)
In this verse, Jesus proclaimed the biblical principle of calling those things that be not as though they are. He said that when you ask God for something, you must believe you have already received it, and after you believe you have received it, then you will receive it. Of course, in order to believe it, you must first conceive it and see it mentally. It is virtually impossible to believe for victory without mentally seeing it first.
That’s what believing in the heart and speaking out of the abundance of the heart is: speaking what you are seeing inside. The true power of the spoken word is when your heart believes what God has told you. When your heart believes, the natural result is that you mentally see the promise and you instinctively speak the promise. When Jesus said, “Out of the abundance of the heart the mouth speaks” (Matthew 12:34), He was revealing to us how faith is activated, and the promise is realized.
Now there are those who will take this principle and attempt to believe for things that God has not promised. This is where the full Word of God must be taken into consideration. In other words, scripture is proved with scripture.
First John 5:14 says if we ask anything according to His will, He hears us. The next verse says that when we know He hears us, then we receive what we have asked. So you can see by this verse that He only hears us when we ask for things that are according to His will. This means the principle in Mark 11:24 — believing that you have received and then you will receive — is based upon the condition of 1 John 5:14 that what we ask must be according to His will. In other words, God grants our requests when we believe we have received what He has promised.