Jesus taught that prayer must be with faith (Matthew 21:21-22; Mark 11:22-26) 

In theses verses I see three aspects of faith in prayer that Jesus teaches.  First of all…

(1) Faith must be in God.  Matthew 21:22 says, “Have faith in God.”  Prayer with faith, therefore, is prayer that believes in God and in the promises that He has given us.  Then it is prayer that expects God to answer based on those promises; it is prayer that has a continuing hope for the answer and a lasting energy to pray until the answer comes.  Secondly…

(2) Faith must be with obedience.  Prayer with faith is prayer that doesn’t just pray and then believe that God will do it by Himself without us; it is prayer that counts on God to help us do it; it is prayer that stops praying and starts obeying.

In Mark 11:23 Jesus tells us to do something, to speak to the mountain: “Whoever says to this mountain, ‘Be removed and be cast into the sea’…”

Therefore when we pray with faith we must go and do whatever God tells us to do.  We must act out our faith in obedience.  Hence, there is a point that when we pray with faith we will get up from our prayer position and do what God tells us—obey Him.  If we don’t then our prayers are not of faith.  Thirdly…

(3) Faith must be without doubting.  Jesus said that when we pray we must not doubt in our heart, but believe that those things we pray and ask for will be done for us (Mk. 11:23).  Then He said in verse 24, “Whatever things you ask when you pray, believe that you receive then, and you will have them.”  Here the teaching is not of positive thinking; rather it is having a strong belief and trust in God.  Thus we are to know God so well that we will just know that He will give us what we ask for—and so our knowledge will be based on what we know of His goodness and kindness.  Thus we are to have the faith of a child that thinks his or her father is the best father in the world.  This is faith so expectant, so hopeful in God that we have absolutely no doubt that God will give us what we ask for.  In fact, this faith in prayer claims the things we pray for as already being ours even before we receive them.