Fasting is a biblical idea that doesn’t get talked about very much, perhaps because the biblical witness to it is not very extensive. Our perception is that fasting is used when Christians are serious about some prayer concern, as though fasting puts extra pressure on God to come through.
In Luke 5:33-35 Jesus speaks about the discipline of fasting. Jesus associates fasting with the presence or absence of the Bridegroom. It is obvious that the Bridegroom is Jesus himself and that since he is with the disciples in the present, there is no need for them to fast. Implied is the idea that when he is absent they will or even should fast. What does the presence or absence of Jesus have to do with fasting?
Betrothal and marriage were times of great celebration, and still are. Jesus appears to be speaking of his time with the disciples as the period of betrothal. There was joy and celebration with him there. He then reveals that there would be a period of separation between the betrothal (his first coming) and the wedding (his second). Between the two (the period we are now living in!) would be the time for fasting.
The way the New Testament talks about the believer there is a sense in which we experience both of these realities at once: the presence and absence of Christ. Colossians 3:1-4 speaks of how our life is already hidden with Christ in God. Elsewhere Paul writes of how our souls have been resurrected to newness of life while we await the same for our bodies (the absence of Christ part).
In fasting, we choose to focus upon the life of the soul at the expense of the life of the body. We are effectively saying that while we know we can live for a period of time without physical sustenance, we dare not go without spiritual nourishment. One could even say that if we replace the meal with time of prayer, study or worship, we have chosen to live in the future, a future where our souls already exist and our bodies long to.
From another angle, in fasting we are looking forward to the great celebration of the Marriage Supper of the Lamb (Rev. 19). By choosing not to eat a meal we remind ourselves that no meal or even feast here can compare with the truest feast of all, that feast when we are united soul and body with Christ perfectly and eternally.