In what sense some things are said to be Impossible to the Almighty

In God there is active power, but no potentiality. Now possibility is spoken of both as involving active power and as involving potentiality. Those things then are impossible to God, the possibility of which would mean in Him potentiality. Examples: God cannot be any material thing: He cannot suffer change, nor defect, nor fatigue, nor forgetfulness, nor defeat, nor violence, nor repentance, anger, or sadness.

Again, since the object and effect of active power is some produced reality, it must be said to be impossible for God to make or produce anything inconsistent with the notion of 'reality,' or 'being,' as such, or inconsistent with the notion of a reality that is 'made,' or 'produced,' inasmuch as it is 'made,' or 'produced.' Examples: God cannot make one and the same thing together to be and not to be. He cannot make opposite attributes to be in the same subject in the same respect. He cannot make a thing wanting in any of its essential constituents, while the thing itself remains: for instance, a man without a soul.* Since the principles of some sciences, as logic, geometry, and arithmetic, rest on the formal, or abstract, constituents on which the essence of a thing depends, it follows that God cannot effect anything contrary to these principles, as that genus should not be predicable of species, or that lines drawn from the centre of a circle to the circumference should not be equal. God cannot make the past not to have been. Some things also God cannot make, because they would be inconsistent with the notion of a creature, as such: thus He cannot create a God, or make anything equal to Himself, or anything that shall maintain itself in being, independently of Him. He cannot do what He cannot will: He cannot make Himself cease to be, or cease to be good or happy; nor can He will anything evil, or sin. Nor can His will be changeable: He cannot therefore cause what He has once willed not to be fulfilled.* There is however this difference between this last impossibility on God's part and all others that have been enumerated. The others are absolute impossibilities for God either to will or do: but the things now spoken of God might will and do if His will or power be considered absolutely, but not if it be considered under the presupposition of His will to the contrary. And therefore all such phrases as, 'God cannot act contrary to what He has arranged to do,' are to be understood in sensu composito; but, understood in sensu diviso, they are false, for in that sense they regard the power and will of God considered absolutely.*

2.24 : That God acts by His Wisdom
2.26 : That the Divine Understanding is not limited to certain Fixed Effects