Light and darkness, Spirit and flesh.

References:The Bible Exposition Commentary vol.2 - Warren W. WiersbeBeliever's Bible Commentary - William MacDonaldThe Freedom & Power of Forgiveness - John MacArthurThe Epistles of John - Marshall The Epistles of John - John R. W. StottThe Joy of Fellowship, A Study of John - J. Dwight, PentecostThe Freedom & Power of Forgiveness - David Augsburger