The devils intentions are to destroy God’s plans. The devil is everywhere he thinks he can trick a soul and drive it to hell.
There are certain things that just work together like, peanut butter and jelly, pencil and an eraser, husband and wife, so too does fasting and prayer. One without the other is just not the same and not effective.
The Apostles knew their Jewish prayers and scripture, yet they were fascinated when they saw Jesus pray. They saw something very attractive, but they were not quite sure what.