You are the children of light. That is, there is little danger of thieves in the day time, when it is light. Also watch and have arms to defend you, the coat of mail of faith; the helmet of hope: you are under the protection of Christ, who died for you, and for your salvation. See St. Chrysostom, p. 293 (Witham)
And how is it possible to be sons of the day? Just as it is said, sons of destruction and sons of hell. Wherefore Christ also said to the Pharisees, Woe unto you— for you compass sea and land to make one proselyte, and when he has become so, you make him a son of hell. Matthew 23:15 And again Paul said, For which things' sake comes the wrath of God upon the sons of disobedience. Colossians 3:6 That is, those who do the works of hell and the works of disobedience. So also sons of God are those who do things pleasing to God; so also sons of day and sons of light, those who do the works of light. And we are not of the night nor of darkness.