This refers to the day that the king will lead his armies into battle. This can be stated clearly. Alternate translation: "on the day that you lead your armies into battle" (See: [[rc://en/ta/man/jit/figs-explicit]])
David describes the dew as a baby to whom the dawn gives birth. Alternate translation: "in the morning ... like the dew" (See: [[rc://en/ta/man/jit/figs-personification]])
David is telling the king that he will have youthful strength each morning by comparing it to how the dew appears early each morning. Alternate translation: "each morning you will be filled with youthful strength to sustain you just like each morning the dew appears to water and sustain the earth" (See: [[rc://en/ta/man/jit/figs-metaphor]])