Galatians 4:9 (ESV) — But now that you have come to know God, or rather to be known by God, how can you turn back again to the weak and worthless elementary principles of the world, whose slaves you want to be once more?
So much can be said about this verse. Let's leave the theological implications alone for a moment and take a closer look at the construction of this clause. What strikes me as significant is Paul's flip flop in how he states what he is trying to say in this verse. It is almost as if Paul is having an "Ahh-haa" moment. This is what I see. First, Paul states in the first half of the clause that the Galatians have come to know God. The aorist active participle is an example of the Galatians knowing by experience. In this first half of the clause, Paul is saying that the people have found God. Specifically, they are the ones who did the searching; they are the ones that found; they are the active participants in the relationship and God is a passive participant. In a nutshell, the people are the subject and God is the object.
In the second half of this clause, Paul seems to take a step back from what he just wrote and after examining it changes everything. After putting a little thought into it, Paul says that the people are not the subject, but God is the subject. God is the active participant. The people are the recipients. The people are not the ones who have come to know God, but rather they have come to be known by God. This is a shift in subject and object.
The implications are simply that we should be sure to recognize that God is the subject of the activity. We don't come to know God. We don't do this or that for God. God, as the subject, actively works in our lives.