“For who has known the mind of the Lord, or who has been his counselor?” (ESV)
I have heard people say things like, "When I get to heaven I am going to ask God a lot of questions." They make this statement almost as if God has some explaining to do for how he has conducted himself as the God of this universe. This is, of course, a very foolish position to place oneself in. When we are in God's presence we will act with absolute humility and reverence.
It is fascinating that the Apostle Paul is here quoting the prophet Isaiah. Isaiah knew that those who had seen the Lord did not act as if they were in any position to be the Lord's counselor. How did Isaiah know this? Isaiah had a vision in which he saw the Lord. Take special note of how Isaiah responded to the very presence of God in Isaiah 6:4-5:
 And the foundations of the thresholds shook at the voice of him who called, and the house was filled with smoke.  And I said: “Woe is me! For I am lost; for I am a man of unclean lips, and I dwell in the midst of a people of unclean lips; for my eyes have seen the King, the LORD of hosts!” (ESV)
This does not sound like a scenario in which Isaiah is going to give God any kind of instruction. Rather, a genuine encounter with the Lord Almighty seems to produce in man a very real recognition of sinfulness. Who has known the mind of the Lord? Who has been his counselor? No one! We are in awe and praise of his eternal greatness.
We will never understand all of the Lord's ways. They are so far above us. This should give us cause to worship and glorify him. He is holy. We are nothing without him.