By St. Gregory Palamas
That incorruptible body was fed after the resurrection, not because it needed food, but to prove it had risen and to demonstrate that it was the same one as He had eaten with them before the passion. It did not, however, consume the food in the way that mortal bodies do, but by divine energy, as, so to speak, fire dissolves wax, except that fire has to have fuel to sustain it, whereas immortal bodies do not need food for sustenance.
The piece of baked fish and the honeycomb which He ate were also symbols of Christ's mystery. The Word of God united Himself hypostatically with our human nature, which was like a fish swimming in the waters of pleasure-loving, passionate life. By the unapproachable divine fire of His Godhead He cleansed this nature of every tendency towards passion, and made it equal to God, and, as it were, red hot. The Lord came to send fire upon the earth (cf. Luke 12:49), and through participation in this fire He makes divine not just the human substance which He assumed for our sake, but every person who is found worthy of communion with Him. On the other hand, human nature is like honeycomb because we hold the treasure of reason in our bodies, just as honey is contained in the comb. This is especially true of anyone who believes in Christ, for he has the grace of the divine Spirit stored up in his soul and body like honey in wax. The Lord ate these things because He was pleased to take the salvation of each human being as His food. He did not, however, eat it all, but just a piece of a honeycomb, that is, a part of it, for not everyone believed. Nor did He take this portion Himself, but it was given Him by His disciples, for the disciples set before Him just the believers, separating them from the faithless.
By eating the fish and the honeycomb in front of His disciples, in this way and for these reasons, He reminded them of the words He spoke to them previously when He was approaching His passion, thus proving that He was truthful.
From Homily 21, "On the Ascension of our Lord and God and Savior", Saint Gregory Palamas the Homilies.