‘But he who does what is true comes to the light, that it may be clearly seen that his deeds have been wrought in God'.
On the other hand those who do what is right have no fear of the truth about their lives coming out. They gladly come to Jesus and listen eagerly to His words and to the word of God and let Him examine them, for they know that His words will help them get rid of sin and that when He examines them He will help them rid themselves of what is spoiling their lives. They want their lives to be open to examination and be put under the spotlight of God, so that what they really are can be seen, that they are true children of God.
‘That it may be clearly seen that his deeds have been wrought in God'. Such a man's conscience is totally clear. He does not mind that his life is brought into the light, for he knows that anything he had of which he should be ashamed has been dealt with by the blood of Christ, and that now he is so living that there is nothing to be ashamed of. Thus he is happy for anyone to see the light shining from him. As Jesus said elsewhere, ‘let your light so shine before men that they may see your good works, and glorify your Father who is in Heaven'. (Matthew 5:16). But in the end, more importantly, he is happy for God to see what he does so that God will be pleased with what he has done.
‘That his deeds have been wrought in God.' That is that that they have been carried out by one who is committed to God and enveloped in Him by faith, that they are the result of an attitude of obedience which brings them within His sphere. That they have God's full approval as wrought by one who is truly His. They are the consequence of his close walk with God.
But a final word of warning. Coming to Jesus Christ and believing in Him involves coming to the light. Those who continue in darkness may have some kind of belief but it is not the belief in Jesus Christ that saves, for when Jesus saves His work is effective.
Note. Are John 3:16-21 the words of Jesus?
The impression given by the passage is that we do have here the words of Jesus. It is not of course possible to assert dogmatically that those who take another position are not correct, for each must see it as he will. But there is nothing in the passage which is not said elsewhere by Jesus in one way or another. John 3:13-15 are equally 'extreme' in their ideas, and many would not deny them to Jesus. (Some would deny any words to Jesus, but that is another matter).
Nor is there any theology in it that is not spoken elsewhere by Jesus. He elsewhere speaks regularly of 'the Son', which by inference means 'the only Son'. He has already just spoken of His coming death in veiled form (and it is equally veiled in John 3:16. We look on it from the other side of the resurrection).
But a main argument for the position of those who see this as a comment of John's is that here Jesus speaks baldly of 'God' whereas normally He speaks of 'the Father'. However the fact is that God is only mentioned twice in the whole passage, whilst elsewhere Jesus does equally suddenly and baldly say 'God' elsewhere (e.g. John 13:31-32; John 4:10; John 4:24; John 5:42; John 6:27; John 6:33; John 6:46; John 7:17; John 8:40; John 8:47; John 11:4; John 14:1), as He also does in the other Gospels. Yet in all places He is also careful not to overuse the term. Note how He often uses the passive tense so as to avoid saying 'God'. E.g. 'They shall be comforted' rather than 'God will comfort them'. This attitude was especially important when speaking to the Pharisees and strict Jews for they too sought to avoid using the name God as much as possible, while not doing so completely.
But here Jesus is in personal and close conversation with a seeker and wants the idea to come over with full force. Furthermore this is at the beginning of His ministry and we could equally suggest that He had not yet finalised His later way of speaking. So there really is no strong reason for denying that these words are the words of Jesus.
One possibly stronger argument, is that it is difficult to see John 3:35-36 on the lips of John the Baptiser. It was Jesus who spoke of 'the Father' and 'the Son'. But it is one thing to see a small comment at the end of a section as a comment of the author, quite another to argue the same for a much larger portion as here. And besides, John the Baptiser does say some surprising things and had no doubt had many close conversations with Jesus after His baptism.
Whether the author would add words to the words of Jesus in a way that could be so easily misleading is a matter of opinion. But there is a strong case for suggesting that in the early church the words of Jesus were looked on as so important that such a procedure would have been frowned on.