“But he answered and said, It is written, Man shall not live by bread alone, but by every word that proceedeth out of the mouth of God.”
King James Version (KJV)
4:4 It is written - Thus Christ answered, and thus we may answer all the suggestions of the devil. By every word that proceedeth out of the mouth of God - That is, by whatever God commands to sustain him. Therefore it is not needful I should work a miracle to procure bread, without any intimation of my Father's will. #Deut 8:3|.
Mt 4:4 But he answered and said, It is written. The Lord uses the sword of the Spirit in his reply. The word quoted, found in De 8:3, should be used in its connection, in order to comprehend its force. But by every word, etc. The meaning is: If it pleases God to sustain by other means than bread, it will be done. His word can be trusted. God fed Israel with manna, sent by his word, and we can trust his promises.