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.
“I have sworn unto David My servant ... with whom My hand shall be established: Mine arm also shall strengthen him.... My faithfulness and My mercy shall be with him: and in My name shall his horn be exalted. I will set his hand also in the sea, and his right hand in the rivers. He shall cry unto Me, Thou art my Father, my God, and the Rock of my salvation. Also I will make him My first-born, higher than the kings of the earth. My mercy will I keep for him forevermore, and My covenant shall stand fast with him.” Psalm 89:3-28. PP 755.1
“His seed also will I make to endure forever,
And his throne as the days of heaven.” Psalm 89:29. PP 755.2
“He shall judge the poor of the people,
He shall save the children of the needy,
And shall break in pieces the oppressor.
They shall fear thee while the sun endureth,
And so long as the moon, throughout all generations....
In his days shall the righteous flourish;
And abundance of peace, till the moon be no more.
He shall have dominion also from sea to sea,
And from the river unto the ends of the earth.”
“His name shall endure forever:
His name shall be continued as long as the sun:
And men shall be blessed in him:
All nations shall call him blessed.” PP 755.3