3:18-23 To have a high opinion of our own wisdom, is but to flatter ourselves; and self-flattery is the next step to self-deceit. The wisdom that wordly men esteem, is foolishness with God. How justly does he despise, and how easily can he baffle and confound it! The thoughts of the wisest men in the world, have vanity, weakness, and folly in them. All this should teach us to be humble, and make us willing to be taught of God, so as not to be led away, by pretences to human wisdom and skill, from the simple truths revealed by Christ. Mankind are very apt to oppose the design of the mercies of God. Observe the spiritual riches of a true believer; All are yours, even ministers and ordinances. Nay, the world itself is yours. Saints have as much of it as Infinite Wisdom sees fit for them, and they have it with the Divine blessing. Life is yours, that you may have a season and opportunity to prepare for the life of heaven; and death is yours, that you may go to the possession of it. It is the kind messenger to take you from sin and sorrow, and to guide you to your Father's house. Things present are yours, for your support on the road; things to come are yours, to delight you for ever at your journey's end. If we belong to Christ, and are true to him, all good belongs to us, and is sure to us. Believers are the subjects of his kingdom. He is Lord over us, we must own his dominion, and cheerfully submit to his command. God in Christ, reconciling a sinful world to himself, and pouring the riches of his grace on a reconciled world, is the sum and substance of the gospel.

18. seemeth—that is, is, and is regarded by himself and others.

wise in this world—wise in mere worldly wisdom (1Co 1:20).

let him become a fool—by receiving the Gospel in its unworldly simplicity, and so becoming a fool in the world's sight [Alford]. Let him no longer think himself wise, but seek the true wisdom from God, bringing his understanding into captivity to the obedience of faith [Estius].