“I have become mute, I do not open my mouth, because it is You who have done it.” (Psalm 39:9)
Although we do not know the exact nature of it, David was in a life crisis here in Psalm 39. He said in :2, “my sorrow grew worse”, and in :3 “my heart was hot within me”, and he spoke of the “plague” that was upon him in :10. There are also indications that the problems that had come upon him were a result of his own sin: in verse 8 he said, “Deliver me from all my transgressions” and in :11 “With reproofs You chasten a man for iniquity.”
Perhaps as a result of the self-inflicted nature of what he was experiencing, David decided to keep his mouth closed about what was happening to him, saying here in :9, “I have become mute, I do not open my mouth.”
David realized that he deserved what was happening to him, so he did not complain about it. He also knew that God was behind it: “it is You who have done it”, he said here, and he spoke of “Your plague” and “the opposition of Your hand” in :10, and how “You chasten a man for iniquity” in :11. So he didn’t raise objections about it to the Lord.
This is not a bad tack to take, even in situations different from David’s, in which we have not brought evil upon ourselves. Sometimes it is just obvious that God has done something (as in :9 here “it is You who have done it”) and there is nothing you can do about it. It is obviously His will, and nothing you can say or do will change it. He is God and you are not — and sometimes we just have to accept His sovereign will. (We do also have the comfort of knowing that whatever He does is wise and good, whether we understand it at the time or not!)
The Lord is not averse to our protestations. In fact, J.I. Packer has identified a whole class of Psalms he calls “complaint Psalms” — almost 20 of them — so it is definitely not wrong to share our hearts with God. But there are also times, as in David’s life here, when it is best for us to join Job, who said in 40:4, “Behold, I am insignificant; what can I reply to You? I lay my hand on my mouth.”