The question in the title was asked in a Christian social media forum. The answer I gave, copied here assumes exposure to Christian Tradition. The practice of fasting and prayer has been around for a long time. It is mentioned in the Bible a lot. It is a sign for penance, mourning, focus on prayer for urgent needs, restoration to right relationship with God, and taking up our crosses to follow Christ Jesus. There are many persecuted Christians in the world today. They are strengthened by our prayer and fasting. There are many situations where God is mocked, situations we have little control over. The most powerful thing Christians can do is fast and pray. We have all failed at times to be light in this crooked generation. When we pray, Christ pours out His Mercy and Grace. There are many suffering in the world today. God still heals. God still does miraculous things when we fast and pray. Satan and the other evil spirits prowl the world seeking souls to destroy. By fasting and pray...