William Burkitt on John 6:63

To convince the Jews that our Saviour did not mean a carnal and fleshly eating of his body, he tells them, That such an eating would profit nothing; but it is a spiritual eating of him by faith, that bringeth that quickening life of which he had spoken. It is the spirit, or divine nature, that quickeneth; the flesh, or human nature, alone, separated from his godhead, profiteth nothing, and can give no life.

Learn hence, That it is the godhead of Christ united to the human nature, which adds all virtue, efficacy, and merit, to the obedience and sufferings of the human nature. It is the spirit, or divine nature of Christ, that quickeneth; the flesh, or human nature alone, profiteth nothing; and therefore the carnal eating of his flesh would do no good.