When we think of fasting & praying for 21 days or 3 weeks or 504 hours it can seem quite overwhelming. It could kind of, sort of, feel like a lot of pressure if we are really being honest. What do I eat? What shouldn't I eat? What should I pray for & what shouldn't I pray for? Yet Jesus taught us to pray like this: "Give us this day our daily bread".
#1. "Give us" We are asking of Him. So that takes the pressure off of us. We know that only He can supply what we need.
#2. "This day" He knows our day. He knows the day we live in & He knows the next 21 days.
#3. "Our" this bread is tailor made for us. Your bread and my bread might look totally different because God meets us where we are at.
#4. "Daily Bread". He wants to pour out provisions that only heaven can supply. Daily answers, tiny morsels of revelation prepared just for us. There are sentences that He wants to speak specifically over us each day. Words of affirmation and encouragement.
All we have to do is relax and rely on Him moment by moment and all the pressure will seem to disappear. I don't think there is a greater way to please the Lord than by placing our trust in Him for each moment of our day for the next 21 days while expecting Him to lead us.