Paul appeals to their conversion experience. All those who know Christ’s converting power have consciously received the Spirit of God, for conversion is not possible without the Spirit coming to dwell within us forever.
It is remarkable that even on such a momentous occasion, the Spirit does not draw attention to himself but to Christ. As he comes to dwell in us, it is Christ we are conscious of. The Spirit recedes into the background and teaches us the wonder of what Christ has done for us and magnifies him in our eyes. He makes us aware that we are accepted in the beloved, and makes us love God’s word as a rock on which we can build our lives. The Spirit enables us to see the state of this world and to separate ourselves from its influence. But none of this comes to us from the law; there is no sense in us that we deserved these things.
All Christians are aware that they have received the Spirit, but that does not mean that they will never ask the question, ‘Have I received the Spirit?’, for when the Spirit is grieved, he may withdraw and remove the felt comfort of his presence within us. If so, we cannot fabricate a sense of his presence, nor can we store up his blessings in advance and draw on that store when trouble comes, for like the manna which bred worms when kept till the next day (Exodus 16:20) the comfort of the Spirit must be enjoyed immediately and cannot be kept for the future.
Paul appeals to Christian experience here in a way that may surprise us, for he seems to argue that we may determine the truth of the gospel by personal experience. Does he set experience above the word of God, or to give it the same authority as the Scripture? Surely the doctrine of justification by faith must rest on a firmer foundation than that. However there is such a thing as true Christian experience and it is defined by God in his word. Ultimately we come back to the Scripture, and yet genuine experience at conversion is a powerful teacher to the individual believer, as long as it conforms to the Bible.