For God, who commanded the light to shine out of darkness, hath shined in our hearts, to give the light of the knowledge of the glory of God in the face of Jesus Christ. For God, who commanded the light to shine out of darkness - The apostle refers here to Genesis 1:3. For when God created the heavens and the earth Darkness was on the face of the deep; and God said, Let There Be Light; and there was light. Thus he caused the light to shine out of darkness.
Hath shined in our hearts - He has given our hearts the glorious light of the Gospel, as he has given the world the glorious light of the sun. As sure, therefore, as God is the author of the light and the creator of the universe, so sure is he the author of the Gospel; it is no human invention; and is as far beyond the power of man's wisdom and might, as the creation of the world is beyond all created power, energy, and skill.
The light of the knowledge - To give us that light, that we might enlighten others; this appears to me to be the design of the apostle's προς φωτισμον της γνωσεως της δοξης του Θεου, or, as Dr. Whitby paraphrases it, to give us, and enable us to give to others, the light of the knowledge of God through Christ.
In the face of Jesus Christ - It is in and through Jesus that we can receive the Divine light, and it is in and by him that we can be made partakers of the Divine glory. The light mercy, holiness, and glory of God, are reflected upon and communicated to us through Jesus the Christ; and it is εν προσωπῳ, in the appearance and person of Jesus Christ that these blessings are communicated to us.