Possible meanings are that God's hand is 1) a metonym for his guidance, his power, or his protection. Alternate translation: "you will guide me" or "you will make me prosper" or "you will protect me" or 2) a synecdoche for himself. Alternate translation: "you will be with me" (See: [[rc://en/ta/man/jit/figs-metonymy]] and [[rc://en/ta/man/jit/figs-synecdoche]])
The words "his prayer" are a metonym for what Jabez asked in the prayer. Alternate translation: "did what Jabez had asked him to do" (See: [[rc://en/ta/man/jit/figs-metonymy]])