This is still the farm illustration strictly speaking. These words are life-giving instructions from the father to the son on how to run everything.
What is the application of the picture? Well the application is first this: salvation alone is life, and health. The salvation of God, conversion to Christ, the washing away of sin, and the new birth which God can give, when we repent of our sins and come to him, this alone gives spiritual life, eternal life, and meaningful life. And this alone brings us into touch with God, so that we are able by prayer to cry out to him, and the application of his word to cope with all the blights and problems that come along. There is no comfort in tragedy and on a deathbed for a person who does not have Christ. There is no meaningful, deep way of coping with all the different things that happen in life without him. This salvation, and the blessing of God, and the wisdom of God, alone are life and health.