Biblically, fasting is abstaining from food, drink, sleep or sex to focus on a period of spiritual growth. Specifically, we humbly deny something of the flesh to glorify God, enhance our spirit, and go deeper in our prayer life.
Fasting is not a kind of work required by the commanded by Christ or required by the scripture. However, that does not mean that fasting is not recommended as part of our spiritual growth. Acts 13:4; 14:23notes believers who made important decisions after fasting. Fasting and prayer are always linked together (Luke 2:37; 5:33).
The purpose of fasting is to take our eyes off the things of this world and instead focus on God. Fasting is a way to demonstrate to God and to ourselves that we are serious about our relationship with Him. Although fasting in Scripture is almost always a fasting from food, there are other ways to fast. Anything you can temporarily give up in order to better focus on God can be considered a fast (1 Corinthians 7:1-5). Fasting should be limited to a set time, especially when the fasting is from food. Extended periods of time without eating are harmful to the body. Fasting is not intended to punish our flesh, but to focus on God
In relation to Matthew 17:21, there are some things that may never work out until that moment when you take time off and seek the Lord deeply through fasting and prayer. The period of the fast has to be decided by you and through the fasting period; the Holy Spirit takes you through as ministers to you. This should be the life of a servant living: to deny yourself for God is sacrificial lifestyle before God.
In Isaiah 58; we learn what a "true fast" is. It's not just a one-time act of humility and denial before God; it's a lifestyle of servant ministry to others. As Isaiah tells us, fasting encourages humility, loosens the chains of injustice, unties the chords of the yoke, frees the oppressed, feeds the hungry, provides for the poor, and clothes the naked. This concept of fasting isn't a one day thing - it's a lifestyle of servant living for God and others. What happens is marked noted in Isaiah 58:8-9
The benefits of fasting and prayer are not general but vary from person to another depending on reasons that make you fast and this is evidenced through testimonies.
Lastly, if something is not working out in your life, take it to God through fasting and prayer and tell you what! Its gonna be alright. So go for it!!....