This verse is often quoted when speaking of doing the work of God, and doing so follows a correct spiritual principle. When God does something, it is not done through physical strength. It is interesting that might literally means "arms," and power refers to physical activity. The work of God is not going to be done through feats of arms, military victories, or anything that requires physical fighting or contention. Nor can it be accomplished by any amount of physical activity.
As much work and effort as men put into it, they are not what will get God's work done properly. They will be helpful, certainly, because God works though men, and men must exert themselves in order to do God's will. Nevertheless, He says clearly here that all the credit goes to His Spirit. God Himself is at work! Our job is to submit, to do the things that must be done. We must do what the Spirit directs us to do, but God will receive the credit, not us. We could do none of these works by our own means.
God gives the ability. He gives the inspiration, the strength, and the endurance. He opens the doors. He supplies the manpower, the money, and the other resources to go through those doors. He supplies favor so that the doors can be opened. We merely walk through them.
We could say that God's work is an act of grace. It is a kind of oxymoron to say that work is done by grace, since we think of work and grace as two extremes, but they are not! What comes first? The grace comes first: God grants favor and gives gifts, then the work is done. So where is the glory? It appears in the grace. The effort comes afterward and accomplishes God's will.