The sermon delivers a sobering warning against spiritual apostasy, using Isaiah's prophecy of a diminished harvest and scattered gleanings to illustrate God's judgment on those who abandon Him for false securities. Central to the message is the recurring theme of 'strange slips'—human efforts, self-reliance, and worldly pursuits mistaken for faith—contrasted with the true, divinely ordained planting of the gospel, which bears fruit only through grace, not human effort. Drawing from Scripture, including Jeremiah's lament over Israel's idolatry and the tragic fate of Aaron's sons who offered strange fire, the preacher emphasizes that God demands exclusive devotion and warns against adding to or altering His revealed Word. The ultimate hope lies not in national Israel or earthly achievements, but in the church—the true Israel—where the mystery of God's eternal purpose in Christ is revealed and sustained by the Spirit, not human wisdom. The final call is to abandon all false refuges, trust in Christ as the sure foundation, and rest in His Word, which alone endures the coming flood of judgment.