פירוש על תהילים 45:5

for the sake of truth To instruct according to the law and to behave with righteous humility.

and it shall instruct you The Torah and the matter of truth in which you shall engage shall teach you tactics of war so that your right should perform awesome things. Since he mentions the study of Torah in an expression of war, the expression of the right hand, prepared to fight, is appropriate (i.e., it is customary to fight with the right hand).