Don't work for the food which perishes, but for the food which remains to eternal life, which the Son of Man will give to you. For God the Father has sealed him."
It is a frivolous exercise of ingenuity to infer, as some do, from the word labor or work, that we merit eternal life by our works; for Christ metaphorically exhorts men, as we have said, to apply their minds earnestly to meditation on the heavenly life, instead of cleaving to the world, as they are wont to do; and Christ himself removes every doubt, when he declares that it is he who giveth the food; for what we obtain by his gift no man procures by his own industry. There is undoubtedly some appearance of contradiction in these words; but we may easily reconcile these two statements, that the spiritual food of the soul is the free gift of Christ, and that we must strive with all the affections of our heart to become partakers of so great a blessing. 