Blank checks are nice, especially when they are given to us and are not associated with our account. An even nicer situation is when this is true and the implication is write in what is needed!
Consider this blank check:
Matthew 7:7-11  “Ask, and it will be given to you; seek, and you will find; knock, and it will be opened to you.  8 “For everyone who asks receives, and he who seeks finds, and to him who knocks it will be opened.  9 “Or what man is there among you who, when his son asks for a loaf, will give him a stone?  10 “Or if he asks for a fish, he will not give him a snake, will he?  11 “If you then, being evil, know how to give good gifts to your children, how much more will your Father who is in heaven give what is good to those who ask Him! 
Does this passage and others really give us a “blank check” regarding prayer? Yes and no. It is important to know the symphony of biblical teaching regarding a topic so we do not come to the wrong conclusion. We truly are given a “blank check” in prayer to our Heavenly Father if the following truths are simultaneously being practiced: 
  • Pray for spiritual growth in kingdom living (Matthew 5-7). Matthew 7:7-11 is embedded in the “Sermon on the Mount” where Jesus is calling for a certain kind of life. Within the context He is saying “ask, seek, knock” in regard to living these truths out.
  • Pray believing that God will answer (Matthew 21:22; Mark 11:24; James 1:6)
  • Pray knowing that your heavenly Father already knows (Matthew 6:8)
  • Pray knowing that your prayers are only acceptable before God because of Jesus (John 14:13; 14:14; 15:16)
  • Pray according to the will of God (John 15:7; 1 John 5:14)
  • Pray with the right motives (James 4:3)
  • Pray as you live in obedience (1 John3:22; 1 Peter 3:7)
  • Pray knowing your joy depends on it (John 16:24)
  • Pray knowing that your prayer or lack of prayer matters (James 4:2)
  • Pray knowing that God is able to do abundantly beyond all that we ask or think (Ephesians 3:20)

So is prayer a blank check? Yes. But it must be “cashed in” according to these biblical truths regarding prayer. It is possible to “pray” without regard to these truths and be “bouncing checks.” Certainly it is much better to take part in this privilege of prayer as God has set it up. As you pray in these biblical ways God will encourage you in your prayer life by showing you how He is incorporating your prayers to carry out His eternal purposes. There is no greater joy than to have God, the One in whom is the fullness of joy, using you to carry out His purposes in prayer.