D.A. Carson

SPIRITUAL WARFARE: The Armor of God: ALL PRAYER and SUPPLICATION: Part – 8 of 15

Faith is not something we dredge up and psych ourselves up to believe enough to be heard of God; faith is a gift from God (EPH 2:8; ROM 12:3; ROM 10:7). Faith is granted by God and is the vehicle by which the believer responds to the Word of God, as demonstrated everywhere in the Bible, Old Testament and New alike.
Faith exercised will grow and become stronger (just as muscles will in our bodies). If we lack any degree of faith, know it only takes a mustard seed-size of faith to move mountains, for even a tiny faith like this, in an awesome and Almighty God as we serve can accomplish such a thing! If we have unbelief in the midst of our faith, confess this to the LORD and He will deal with it (HEB 11:6; MATT 17:20; MARK 9:24)! Note that the prayer life may be hindered by unforgiveness for others.
Righteousness is another condition for successful prayer