Fasting was a regular practice for strict Jews, although there was only one day of the year where every Jew had to fast and that was on the Day of Atonement, the day when the whole nation confessed their sin and was forgiven. The stricter Jews would generally fast on two days every week-Mondays and Thursdays-from 6 am to 6 pm. Although generally fasting can be seen as a good thing, the Pharisees used it as a means of self-aggrandisement, calling all those who were bystanders to their goodness because they would whiten their faces and wear different clothes on their fast days! They also felt that it would bring them to the notice of God.
So, Jesus is approached and questioned by the disciples of John the Baptist as to why His disciples didn't fast. I think we can understand it to be a gentle, but critical approach, but it can be noted that those who didn't or couldn't fast (because they had jobs full of hard labour) stood out as being 'less religious'. The answer of Jesus involved Him talking about Jewish weddings. When a couple got married, they remained at home and, for a week or so, they had open house where there was continual feasting. I think we can gather from John's description of the wedding in Cana that these were times of great joy and involved the whole community: they were a great escape from what was generally a hard life with an early death. The disciples were like the closest friends of the Bridegroom and so Rabbinic ruling stated that they were relieved of all religious observances during this time of celebration. This is a reminder to us that the life that is lived in Christ cannot be lived other than in joy.
However, Jesus gives the listeners early notice that one day there would be separation and sadness. Jesus knew that the cross lay ahead, yet He wouldn't be deflected from the road He was on.