Thou hast a mighty arm - Margin, as in Hebrew,” an arm with might.” That is, Thou hast great power - the arm being the instrument by which we accomplish our purposes.
Strong is thy hand - The hand, too, is an instrument by which we execute our plans. Hence, God is so often represented a having delivered his people with a strong hand.
And high is thy right hand - It is by the right hand particularly that we carry out our purposes. We lift it high when we are about to strike with force. All this is expressive of the divine omnipotence.