Do not create unnecessary trouble. David and Moses are two larger than life heroes of the Old Testament. In Exodus 5 we find Moses approaching Pharoah to release the Isrealites from slavery. He simply told Pharoah that he was to let the people go. That is the second point.
Smooth stones fly straight.
How many times at work or in the church have you heard someone complain about a specific problem. Before you know it, the original problem is almost forgotten because now the issue has turned to a debate over personalities and who has insulted whom. Smooth stones fly straight to the target. They do not create unnecessary trouble. In these verses are the 3rd and 4th smooth stones.