"Prayer is about as central to the meaning of the created universe as you can get. God created us, according to Isaiah 43:7, for His glory...which we now see means that He created the universe so that persons created in His image would look to Him to satisfy all their wants and needs so that they would get the joy and God would get the glory. When we express this looking to God, we call it prayer."

"God ordains prayer because He wants us to see Him as gloriously self-sufficient and ourselves as totally needy." 

- John Piper, Devote Yourselves to Prayer

"The prayer of the upright is His delight." - Proverbs 15:8

"For what great nation is there that has a god so near to it as is the LORD our God whenever we call on Him?" - Deuteronomy 4:7

"It will also come to pass that before they call, I will answer; 
and while they are still speaking, I will hear." - Isaiah 65:24

"On your walls, O Jerusalem, I have appointed watchmen; all day and all night they will never keep silent. You who remind the LORD, take no rest for yourselves; and give Him no rest until He establishes and makes Jerusalem a praise in the earth." - Isaiah 62:6-7

"Call upon Me in the day of trouble; I shall rescue you, and you will honor Me." - Psalm 50:15

"Whatever you ask in My name, this I will do, that the Father may be glorified in the Son." - John 14:13