Summa contra Gentiles2.7 Chapter VII. That in God there is active power

It follows from this that God is powerful, and that active power is fittingly ascribed to Him.

For active power is the principle of acting on another as such. Now it becomes God to be the principle of being to other things. Therefore it becomes Him to be powerful.

Moreover. Just as passive potentiality is consequent upon being in potentiality, so active potency is consequent upon being in act: for a thing is active because it is in act, and passive because it is in potentiality Now it becomes God to be in act.' Therefore active power is becoming to Him.

Again. The divine perfection includes the perfection of all things, as was proved in the First Book. Now active power belongs to the perfection of a thing: since a thing is found to be the more perfect in proportion as it is more powerful. Therefore God cannot be devoid of active power.

Further. Whatever acts, has the power to act, since that which has not the power to act, cannot possibly act; and what cannot possibly act, of necessity does not act. Now God acts and moves, as was proved above. Therefore He has the power to act; and active but not passive potency is fittingly ascribed to Him.

Hence it is said in the psalm Thou art mighty (potens), O Lord, and elsewhere: Thy power and Thy justice, O God, even to the highest great things Thou hast done.