31 “And in the meanwhile His disciples besought Him, saying, Master, eat.” For they had gone to buy meat, and had returned. “But He said, I have meat to eat which you know not of. Therefore said the disciples one to another, Hath any man brought Him anything to eat?” What wonder if that woman did not understand about the water? See; the disciples do not yet understand the meat. But He heard their thoughts, and now as a master instructs them, not in a round-about way, as He did the woman while He still sought her husband, but openly at once: “My meat,” says He, “is to do the will of Him that sent me.” Therefore, in the case of that woman, it was even His drink to do the will of Him that sent Him. That was the reason why He said, “I thirst, give me to drink;” namely, to work faith in her, and to drink of her faith, and to transplant her into His own body, for His body is the Church. Therefore He says, “My meat is to do the will of Him that sent me.”
Source: Tractates on the Gospel of John (New Advent)