Consider this famous verse from 1 John:
Beloved, let us love one another, because love is from God; everyone who loves is born of God and knows God (4.7).
What does it mean to be a Christian, according to John? The answer has to do with metaphysics, epistemology, and ethics; in other words, part of it has to do with your being, your existence, and part of it has to do with what you know and believe and think, and part of it has to do with how you act. All three of these elements come together to comprise a Christian life, according to John.
From the point of view of metaphysics, John says that a Christian has been born of God. There has been a special kind of inner transformation and change brought about by God's causality. Just as a child is born and brought into life through the causality of the mother's body, so also in some mysterious way, God has brought the Christian into life. This might be called being "born again," which is the language Jesus uses in John 3.
This transformation also has an epistemological dimension. John says the Christian is one who knows God. A new understanding of ourselves and our relation to the world in which we live is born when we come to know God as he really is. I think to a great extent, our thinking about God reflects the way in which we see ourselves and other persons. For the Christian, there is a new familiarity with God and acquaintance with him.
Yet the metaphysical and the epistemological, according to John, serve the ethical. The inner transformation accomplished by God's agency and the new awareness and knowledge of God are oriented towards bringing the Christian into a life of love. All these changes take place so that the Christian will begin to live her life in love for God and others. We might say that love is the final cause of the salvific process.
The ethical is the ultimate element, according to John, and therefore serves as the criterion by which to judge a person's progress. He says, Whoever does not love does not know God, because God is love (v. 8). If a Christian fails to love, this is evidence enough that something has gone wrong in the process of her salvation; in the specific case considered by John, it is because she has a deficient understanding of God's character.
It would be interesting to ask whether the metaphysical is prior to the epistemological, so that an inner transformation brings about a new knowledge of God, or if the epistemological is prior to the metaphysical. But this is not the question which John pursues. His only concern is that the children are brought to life, that they are not stillborn. This ought to be our emphasis, too: to live in love, because this is what God saves us towards.