Four and six
Four signifies celestial good, and six, spiritual good; for four signifies conjunction, and intimate conjunction with the Lord occurs when we love Him; but six signifies communication, and communication with the Lord is manifested by charity towards the neighbor.
(References: Apocalypse Explained 283)
2 Corinthians 4:6
6
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.