The relationship between "tremble" and "fear" and who people should fear can be stated clearly. AT: "Fear Yahweh so much that you tremble" or "Stand in awe of Yahweh" (See: [[rc://en/ta/man/translate/figs-explicit]])
The heart represents a person's thoughts. Thinking carefully is spoken of as meditating in one's heart. AT: "Think carefully" (See: [[rc://en/ta/man/translate/figs-metonymy]])