"We give thanks to You, O God, we give thanks!" Psalm 75:1
Gratitude and thanksgiving always look back at the past, though they may also take in the present. But prayer always looks to the future. Thanksgiving deals with things already received. Prayer deals with things desired, asked for, and expected. Prayer turns to gratitude and praise when God has granted the things asked for.
Taken from the book The Best of EM Bounds EM Bounds 1835-1913