"Trust" means to "wholly and securely rely upon God's wisdom, power, and goodness" - not trusting in "creature enjoyments" like wealth or personal wisdom. "Lean not on understanding" warns against depending on "the strength of thine own wit without God's blessing" since human understanding is "darkened by sin" and limited. "In all thy ways acknowledge Him" means seeking God's guidance in every aspect of life. By trusting God completely, "He shall direct thy steps" toward safe and good paths.
This represents a "fundamental principle of all religion" - total reliance on God (BibleHub Commentaries).
