This concursus is represented first, as general; an influence of the omnipresent power of God not only sustaining creatures and their properties and powers, but exciting each to act according to its nature. It is analogous to the general influence of the sun which affects different objects in different ways. The same solar ray softens wax and hardens clay. ... (Charles Hodge, Systematic Theology, 1:599)
Concursus, therefore, assumes, (1) That God gives to second causes the power of acting. (2) That He preserves them in being and vigour. (3) That He excites and determines second causes to act. (4) That He directs and governs them to the predetermined end. ...
The doctrine of concursus does not deny the efficiency of second causes. They are real causes, having a principium agendi in themselves. (1:600)
The above statement of the doctrine of concursus is designed merely to give the views generally entertained by Augustinians, as to the nature of God's providential government. Whether those views are correct or not, it is important that they should be understood. It is very evident that there is a broad distinction between this theory of concursus and the theory which resolves all events, whether necessary or free, into the immediate agency of God. The points of difference between the two theories are, (1.) That the one admits and the other denies the reality and efficiency of second causes. (2.) The one makes no distinction between free and necessary events, attributing them equally to the almighty and creative energy of God; the other admits the validity and unspeakable importance of this distinction. (3.) The one asserts and the other denies that the agency of God is the same in sinful acts that it is in good acts. (4.) The one admits that God is the author of sin, the other repudiates that doctrine with abhorrence. (1: 603)
God works, and there are real second causes at work. To deny the real validity of second causes, like Vincent Cheung, is to make God a monster.