We can add nothing to all that God has done for us once and for all in Jesus. Everything is already DONE. However, the God who has done all for us now calls us to DO whatever he wants us to do. Because God loves us, he desires a response to his love. He even tells us the kind of responses he wants within the relationship he has already given us by grace. For example, the God who has loved us and done all for us calls us to walk in love as dearly loved children. We don’t try to earn his love by loving. We know that we are already deeply loved and so we now aim to live lives of love as God has loved us in Jesus.
All our responses to what God has done for us in Jesus are made possible only because of what God is still DOING within us by his Spirit. At the very core of our persons God is at work within us to freely and gladly will and work for his good pleasure. So, Paul can say, I no longer live but Christ lives in me. Yes, Jesus himself lives his own life of love in and through us, so that we are now able to love with his love.
Furthermore, Jesus not only lives in us, we also live in him. The Spirit has joined us to Jesus lifting our lives into his life. So now, all our imperfect responses are taken into his perfect responses before the Father. In living union with Jesus, we share in the perfect responses that he has made and continues to make for us.