William Burkitt on Luke 4:2

Observe here, how the divine power upheld Christ's human nature without food. What Moses did at the giving of the law, Christ doth at the beginning of the gospel, namely, fast forty days and forty nights. Christ hereby intended our admiration rather than our imitation; or if our imitation, of the action only, not of the time.

From this example of Christ we learn, that it is our duty, by fasting and prayer, to prepare ourselves for a conflict with our spiritual enemies. As Christ prepared himself, by fasting, to grapple with the tempter, so should we.