Prayer is the most important and powerful relational command to the believer. It is our communication with God regarding His promises and our unified position against the attacks of Satan.
Matthew 18:19 (NIV) Again, truly I tell you that if two of you on earth agree about anything they ask for, it will be done for them by my Father in heaven.
1 John 5:14 And this is the confidence that we have toward him, that if we ask anything according to his will he hears us.
Philippians 4:6 (NIV) Do not be anxious about anything, but in every situation, by prayer and petition, with thanksgiving, present your requests to God.