We should always keep in mind the role of the Holy Spirit in sealing each person. It is by the Holy Spirit that we gain conviction in salvation, resurrection, and to save souls.
As we live the life of faith sincerely, our confidence in our salvation in Christ should grow. That is because the Holy Spirit puts conviction into our conscience and heart, that there has been a turning point, and that my old sinful existence is over and my new existence in Christ is here.
Furthermore, the Spirit of truth teaches us about the faith of resurrection. Jesus Christ died and resurrected in order to lead the way as the firstfruits, in order that we may follow as latter fruits who resurrect surely with a glorious body in the future. We gain the firm faith of resurrection, which nothing can overcome and that is stronger than death.
Our life in Christ is not in vain, but is going toward the glorious cosmic change of the entire world. And we have this personal assurance that nothing can separate us from the love of Christ, because we will be clothed with the new body at our resurrection, and be together with Him in glory. The faith of the apostles was such that they even had confidence of living clothed with the spiritual body as they lived in this lifetime–what a powerful witness and faith! But although our resurrection is in the future, it is a really powerful faith and hope that makes us alive today, because our resurrection is not a concept or vague hope. Our resurrection is a concrete conviction that we will rise for sure just as the Lord did in history.
All of these are given to us in the Holy Spirit as a gift in our faith. And these give us the conviction to save souls powerfully. We want to share these gifts of conviction with the many thirsty souls of this world.