The bible suggests that we should fast at times (Luke 6:21, 25) and the following reasons help explain when we should sow to our spirit only (Galatians 6:8).
(1) Of course, there are those un-repented souls who fast in vain (Jer 14:11, 12 Zech 7:5, 6), and fasting alone does not justify us (Luke 18:11-14).
(2) And we do not fast to be recognized, exalt ourselves or pleasure our souls at the time to be spent with the Spirit (Matt 6:6 Isaiah 58:3, 4).
(3) The LORD gives a good example to the ignorant but eager house of Jacob (Isaiah 58:5-12).
(4) The Isrealites fasted for direction (Ezra 8:21-23).
(5) Men interceeded with the LORD in an attempt for Him to repent (2 Sam 12:22, 23 Joel 2:12, 14).
(6) The Lord rewarded a repented Ahab; a king who lead the nation of Israel to sin (1 Kings 21:25-29).
(7) And again the Israelites admitted their sin and knew that only God could fight their battles (1 Sam 7:3-8).
(8) Fasting is a time for separation, worship & confession (Neh 1:4-10 & 9:1-3) and when the Lord’s presence is absent (Matt 9:14, 15).
(9) Jesus allowed a multitude of 4,000 to deny the flesh and receive His word for three days before feeding them (Matt 15;32-38).
(10) In Jonah’s day, every last creature fasted (Jonah 3:5-7).
(11) In a complete fast we see there’s no eating or drinking (Esther 4:16).
(12) And, an anointed fast is between us and God (Matt 6:17, 18).
(13) We see Jesus hungered after he fasted (Matt 4:2), for He followed the will of His Father (John 4:31-34) and fasted for power (Matt 17:21).
(14) We also see revelation knowledge by walking with the Lord (Luke 2:36-38).
(15) And finally Paul’s eating was also guided by the Lord (Phil 4:12)