Exodus 15:6,12 shows God’s ‘mighty hand’ to be an expression of his power, or dominion, over earth, and his control of his enemies.
It tells us, “Thy right hand O Lord, glorious in power; thy right hand O Lord, shatters the enemy. … Thou didst stretch out thy right hand, the earth swallowed them.” The ‘outstretched arm’ of God represents his support and strength, or his omnipotence exercised on behalf of those who trust in him.
Since the human arm supports the hand and gives it direction, and through it power is transferred to accomplish particular actions, a wonderful symbolism is established, helping us to get the picture God desires us to understand—the arm of Jehovah shall give strength to any on whose behalf it is used.
“I have found David my servant; with my sacred oil I have anointed him. My hand will sustain him; surely my arm will strengthen him,” are the emphatic words of David concerning God’s protection and guidance over him, as recorded in Ps. 89:20,21, NIV