Again, I write a new commandment to you, which is true in him and in you; because the darkness is passing away, and the true light already shines.
John does not want any to doubt their salvation unnecessarily because of what he just said, so he quickly reminds them of the grounds for their assurance. New believers may not yet have learnt a lot, but at least they know that they have a Father in heaven who forgives them. Elderly believers have the assurance that comes through their many years of knowing God. Believers in the energetic years of their Christian lives grow in confidence and strength as they see the power of God at work in defeating Satan (12-14).Christians must not allow themselves to become affected by the attitudes and behaviour of the unbelievers around them. The ordinary people of the world belong to the age of darkness and make their decisions according to what they want for themselves, whether concerning possessions, activities, achievements, or status. Christians belong to the new age of light, the eternal kingdom where God’s values rule and his will is done. They must make their judgments according to his standards, not the standards of the present ungodly world (15-17).