“For God, who said, ‘Let light shine out of darkness,’ has shone in our hearts to give the light of the knowledge of the glory of God in the face of Jesus Christ.” (2 Corinthians 4:6)
Prior to coming to verse 6 in 2 Corinthians 4 there is verse 5, which reads, “For what we proclaim is not ourselves, but Jesus Christ as Lord, with ourselves as your servants for Jesus’ sake.” Paul is writing that we – those who believed, at that time, in Jesus Christ – were not proclaiming themselves as Lord but they were proclaiming Jesus as Lord. Apparently there was some discussion going around that these Christians were usurping the Lordship of Jesus in favor of elevating themselves among other people. Paul destroys this falsity as he writes that they are proclaiming Jesus as Lord and, as for the Christians' status among other people, they are placed rightly as servants for everyone for the sake of Jesus.
Moving on from verse 5 one can see that Paul is continuing his line of thinking from verse 5 into verse 6 because of his use of the word for. (A quick note here: It continues to be extremely helpful for me and I assume it will be as helpful for you if, when you are reading your Bible, you work to train yourself to look for specific words and phrases, such as for, therefore, so that, because, and so, because of the way they help us follow the flow of thought for the biblical writers.) In verse 6 Paul is building upon what he wrote in verse 5, which is why we must consider that verse prior to moving on to verse 6. Paul writes that God has shone in our hearts to give the light of the knowledge of the glory of God in the face of Jesus Christ. Breaking that down: Paul said that God has illuminated our hearts to give us an awareness of or a knowledge of the glory of God as it is rightly seen in the person of Jesus Christ. And, not only that, but the reason why Paul says that we proclaim Christ as Lord and live as servants for other people for Jesus’ sake is precisely because of what is written in verse 6. God has done something to bring this about. Namely, God has given us a light so that we can see what we once could not see.
God has given us something that we did not have before. This is a monumentally important truth to grab hold of, wrestle to the ground, and make yours. God has given us something that we were blind to. God had done such a work in their lives at that time and continues to do this same work in the hearts of people today so that when we encounter Jesus Christ we encounter the glory of God. We have this knowledge of the glory of God through seeing Jesus but it is not merely the sight of Jesus that brings about this knowledge; it is God’s work to illuminate what was once darkened through our sin by means of our fallen nature in our first father, Adam. Our ability to see correctly has been damaged beyond our ability to repair. Our sinfulness has separated us from God and has made it so that when we see Jesus we do not love him and anything less than love for Jesus is sinful ignorance of the glory of God. However, as we see in verse 6, God has made a way where there was no way before. No amount of us working to see this glory will make it possible without the work of God to show us what we were blind to. In reality, no one ever wants to see anything that they were blind to because they did not know there was anything else there to see. This is why the mercy and grace of God makes all the difference in us. God has shown us what we did not want to see and he has given us knowledge of the thing that we did not know existed. When God performs this work we see Jesus but we do not only see; we experience the glory of God through God by God. We know Jesus as our Lord through the Holy Spirit making it possible.
When a person whose heart that has not been illumined through the work of God sees Jesus, they see him without the glory of God, which is not who Jesus is; Jesus without the glory of God is an idol because Jesus is the glory of God (Hebrews 1:3). They see him as a man who maybe said some things and maybe did some things but this Jesus is definitely not God. However, for the one whom God has shone his light into they see Jesus with the knowledge of the glory of God. We see him as the Lord and thus, as we saw in verse 5, we proclaim him as Lord because that is the only reasonable response to having the Holy Spirit shine a light into our darkened hearts.