The day of judgment is a day that every believer should think much about, because it is the ultimate measure of spiritual authenticity; the whole of life should be seen as a preparation for that day. No one can manufacture Christian character at the last moment, but he will take with him what has been developed in this life. That day will of course be far more searching than any encounter we have with God in this life, but it will be as the same people that we approach him then. We ought all therefore to endeavour to be now what we will need to be in that day.
If we have lived as those who belong to him here, then we can be confident that we will be with him in heaven. It is not easy to be out of step with all around you, and no one is willing to do this unless he has a loyalty to Christ that overcomes all the influence of the world. We are convinced of love in us because we imitate him and we do it where he did it, in the hardest place of all: in the world. Our allegiance to him is stronger than our allegiance to the world, even though it is present and he is absent.
What does ‘Herein’ refer to? The construction is exactly the same as verse 13 where the first result of our loving one another is addressed – that God dwells in us. Here the second result is developed: that our love is perfected. Both verse 13 and verse 17 begin literally with the words ‘In this’ which could be translated ‘This is how’, and refer forward to what follows the conjunction later in each of the verses – ‘because he hath given us of his Spirit’ (verse 13) and ‘because as he is, so are we in the world’ (verse 17).