With whom my hand shall be established - Septuagint: "My hand shall aid him." Luther; "My hand shall hold him." DeWette; "With him my hand shall be continually." Professor Alexander; "Shall ever be present." The idea is, that God would always defend or protect him. He would not merely interpose at times, or at intervals, but he would be his constant protector. His hand would be permanently, or constantly, extended for his aid - as if it were a part of David's own person, or were his own hand, to be used as he pleased. So God is the constant helper of his people. They may rely on his power; they may avail themselves of it, as if it were their own.
Mine arm also shall strengthen him - In using his own arm, he will in fact make use of the strength of mine. The people of God are as really defended as if the strength of God were theirs; or as if they were themselves almighty. The omnipotence of God is employed in their defense, and it will be as certainly exerted in their favor, and as constantly, as if it were their own. It will be no less surely employed in their defense in the hand of God than if it were in their own hand. It will be more wisely employed by him in their behalf than it would be by themselves.

With whom my hand shall be established,.... A promise of God's gracious presence with Christ, as man and Mediator, which is his work; of a communication of grace and strength from him, to carry him through it; and of his supporting and upholding him under it; which hand of his power and grace would be always prepared and ready for him, as the word (a) signifies, and stable and firm with him, so that he should have success in it; the pleasure of the Lord should prosper in his hand; so the Targum,
"for my hands are prepared for his help;''
the Septuagint, Vulgate Latin, and all the eastern versions, "mine hand shall help him"; and which is confirmed in the next words: mine arm also shall strengthen him; in the human nature, subject to and encompassed with infirmities: this shows the greatness of the work of man's redemption, which no creature could effect; it required the arm and power of the Lord to be exerted, and by which Christ was made strong by the Lord, both for himself, and for the working out of salvation for us; which he did when he travelled in the greatness of his strength, standing up under the mighty weight of our sins, and the wrath of God; and yet failed not, nor was he discouraged, till his own arm brought salvation to him; see Psalm 80:17.
(a) "parate erit", Musculus, Muis; so the Targum.

will protect and sustain (Isaiah 41:10),