Every day, we are steeped in cultural influences that have the power to take hold of our souls, and shape our lives in ways that lead us away from God. The ‘world’ plants its own ideas in our minds, and desires in our hearts, about what it means to be healthy, wealthy and happy. Over time, we can find ourselves craving for things that we know cannot ultimately satisfy, and discover that we have formed ungodly habits that seem hard, if not impossible, to break.
As a way of self-denial and ‘taking up our cross’ (Mark 8:34), fasting can help us put our sinful cravings and habits to death; and open us to the same overcoming power of the Holy Spirit that raised Jesus from the dead.
As we look to God, and the power of the Holy Spirit, we can find the strength to resist our temptations. But more than that, we are also asking God to help us “hunger and thirst for righteousness” so that we might be filled (Matthew 5:6).
The discipline of fasting is common in nearly every religion in the world and is mentioned more times in the Bible than baptism.
Other reasons if you still need more:-
Jesus expects us to fast just as much as He expects us to pray. Matt 6:5-6 and 16-17. He says here When you pray and When you fast.
It is God appointed way to humble ourselves.Ezra 8:21. 1 Kings 21:27-29
Fasting is a spiritual discipline that shows God we are serious about deepening our relationship with Him. This is a discipline that has been followed for centuries so it is a time honoured way to connect on a deeper level with our creator God. By denying our physical body, we submit the physical under the lordship of the spirit. It is a longing for more of God, a hungering for the godly life and a desire to seek God with all our heart, mind, soul and strength (2 Chronicles 7:14; Zechariah 7:5; Matthew 22:37)
Fasting and Prayer together is also used when people are in the midst of trouble or feeling overwhelmed and when there is something specific they want a breakthrough in. See Jonah 3. Esther 4:16
How to Fast