Today's Shrove Tuesday and Lent begins tomorrow. There's a growing movement encouraging people to do something positive during the season, rather than give something up. However, many Christians take it very seriously as a time for denying themselves something they enjoy, particularly food.

But why do Christians fast, and what's so significant about fasting in Lent?

1. Jesus says so

In Matthew 6:16, he says: 'When you fast, do not look gloomy like the hypocrites, for they disfigure their faces that their fasting may be seen by others...' Instead, do it in secret; it's between you and God. He doesn't explain what fasting is for, he just assumes people will do it. So there is a strong biblical warrant for this kind of spiritual discipline.

2. We follow in his footsteps

Jesus himself fasted for 40 days (Matthew 4:2, Luke 4:2). The 40 days of Lent are a way of identifying ourselves with him during the days leading up to his crucifixion and resurrection. Denying ourselves a favourite food or some other luxury is a sign we are walking with him to the cross.

3. Fasting is a form of offering

When we deny ourselves something we enjoy, and which it isn't wrong to want, we are saying there is something more important in our lives than purely physical pleasure. If we fast because we're dieting for our health, it's because how we feel and look is more important. Fasting in Lent means that God is more important.

4. It's a spiritual discipline

When we fast, we are exercising our spiritual muscles. When we refrain from a basic physical desire such as eating, we're saying we refuse to be dominated or controlled by the needs of our bodies. If we can deny ourselves food, we can learn to deny ourselves other things too, which may be much more harmful or morally questionable.

5. It reminds us of God

Many of us get through the day without thinking much about God. But knowing we have to be alert and in control of our instincts, having to fight the temptation to indulge in something we enjoy, reminds us of our discipleship and of his reality in our lives.

Most of us, rightly, won't try the 'extreme' fasting practised in some traditions or by the great saints of old. But giving up even small pleasures is a way of drawing nearer to Christ on his way to the cross.

Follow Mark Woods on Twitter: @RevMarkWoods