Romans 13:12 - Matthew Poole's English Annotations on the Holy Bible

The night is far spent, the day is at hand: some, by night and day, do understand the night of Jewish persecution and the day of deliverance and salvation; see Hebrews 10:25. Others, by night, understand the time of ignorance and infidelity; this, he says, is far spent, or for the greatest part it is past and gone: darkness is not perfectly done away in this life amongst believers themselves, 1 Corinthians 13:9,10. By day, they understand the time of gospel light and saving knowledge: so in the next verse, and in 1 Thessalonians 5:5. This, he says, is at hand, or is come nigh; it was dawning upon the world, and would shine brighter and brighter, till it were perfect day. Let us therefore cast off the works of darkness; i.e. all our former sins, which are called works of darkness, here, and in Ephesians 5:11. They are so called, because they are usually committed by those that are in ignorance and darkness; and because some sins, such as he speaks of in the next verse, were wont to be committed in the darkness of the night, men being ashamed of them in the day time: see Job 24:15 1 Thessalonians 5:7. These he exhorts the believing Romans to cast off: the word implieth, haste and hatred, Isaiah 30:22, Isaiah 31:7. And let us put on the armour of light; i.e. all Christian graces, which are bright and shining in the eyes of the world, Matthew 5:16; and which will be as so much Christian armour, to defend us against sin, and all the assaults of Satan.