to fast or not to fast?

The scribes and Pharisees said to Jesus,
"The disciples of John the Baptist fast often and offer prayers,
and the disciples of the Pharisees do the same;
but yours eat and drink."
Jesus answered them, "Can you make the wedding guests fast
while the bridegroom is with them?
But the days will come, and when the bridegroom is taken away from them,
then they will fast in those days."
And he also told them a parable.
"No one tears a piece from a new cloak to patch an old one.
Otherwise, he will tear the new
and the piece from it will not match the old cloak.
Likewise, no one pours new wine into old wineskins.
Otherwise, the new wine will burst the skins,
and it will be spilled, and the skins will be ruined.
Rather, new wine must be poured into fresh wineskins.
And no one who has been drinking old wine desires new,
for he says, 'The old is good." Luke 5:33-39


Why do we need to fast or is it necessary to fast?
Why the disciples of John and the Pharisees do fasting and Jesus' followers do not?
Jesus said, because he's still with them, but soon after he ascended they will fast because they will long to see him again.
We fast not only for the sake that were fasting but because we desire to see Jesus. We abstain for food, for pleasure, for the materials of this world and other things for higher reason. We do good, we help other people, we share our resources to others specially to those who are in need because we see in them the face of Jesus. But more than of all these goodness, kindness is love, that we become like Jesus in others.
We sacrifice, we abstain because of the higher good, and that higher good is God.