I’ve not grown up with a history of spiritual fasting but recently I have become more interested. This is because when my church fasted ahead of some big decisions I had reason to think about it for myself. One reason for fasting is seeking repentance. This happens in 1 Samuel 7:6 where, commanded by Samuel the people of Israel needed to repent before God after they had turned their backs on Him.
Another reason for fasting is when seeking guidance as was the case with my church at this time. In Nehemiah 1:4, the prophet on hearing the news of destruction in Jerusalem sat down and wept and fasted.
When a revelation from God is desired the people can fast in order to seek His will for them.The disciples of John the Baptist fasted and prayed as we see in Luke 5:33 in preparation for what was ahead of them. Jesus told the Pharisees that His disciples would fast when He was taken away from them which would be in preparation for their future ordeals.
Fasting is not a way of manipulating God but of drawing closer to Him.