Martin Luther (German priest and reformer)

None can believe how powerful prayer is, and what it is able to effect, but those who have learned it by experience.

Charles Spurgeon (British preacher)

I know of no better thermometer to your spiritual temperature than this, the measure of the intensity of your prayer.

From 1 Thessalonians 5:16-18:  “Rejoice always, pray without ceasing, give thanks in all circumstances, for this is the will of God in Christ Jesus for you.”