“The night is far spent, the day is at hand. Therefore let us cast off the works of darkness, and let us put on the armor of light.”

Works of darkness

The works of darkness are clearly described in the following verses, which gratify the desires of the sinful nature – orgies and drunkenness, sexual immorality and debauchery, dissension and jealousy.

Armour of light

The armour of light is explained in verse 14, as to “clothe yourselves with the Lord Jesus Christ”
It’s described in more detail in Ephesians 6:11-13, as the belt of truth, breastplate of righteousness, gospel of peace, shield of faith, helmet of salvation, sword of the spirit (word of God), and prayer.
So, this does not talk of what we need to do in obeying God in terms of refraining from evil deeds, which the history of Israel proved we cannot do in our own strength, but to the choice we have been given of “clothing ourselves with Christ” – to believe in him and accept his free gift of salvation won for us on the cross, which frees us from slavery to our sinful nature.
John 6:29, “The work of God is this: to believe in the one he has sent.”

The night is far spent, the day is at hand

In the past I assumed this referred to the second coming of Christ, for since to God a thousand years are like one day (2 Peter 3:8), the time lag is not important, and we need to be ready for that day.
But I think “the night” may also refer to the rule of darkness, and “the day” the rule of God’s Holy Spirit in this world. Since, as a consequence of Jesus’ victory on the cross, everything has changed for each one of us and for this entire world. We all now have God’s free offer of salvation in Jesus and freedom from slavery to sin, and that is life-changing for each of us right now, and collectively for this world.