This is how we know we’re living steadily and deeply in him, and he in us: He’s given us life from his life, from his very own Spirit. Also, we’ve seen for ourselves and continue to state openly that the Father sent his Son as Savior of the world. Everyone who confesses that Jesus is God’s Son participates continuously in an intimate relationship with God. We know it so well, we’ve embraced it heart and soul, this love that comes from God. (I John 4:13-16 MSG)
Let me begin as John did - genuine faith is evidenced by living steadily and deeply in Christ and he in us! Now, when two are this intimate, there is evidence of the intimacy of the relationship, is there not? Two conditions are present which suggest a level of intimacy. First, it is a steady relationship - there aren't a whole lot of breaks in it. In other words, it is a daily, moment-by-moment thing! When we "go steady" with another person, isn't one of the key ideas of this relationship "status" to be dedicated to the other person and that person alone? I think this is the concept John is getting at here - living steadily, in such a manner so as to show no desire to have any other relationship matter as much to us as does our relationship with Christ. Second, it is a two-way relationship - we are "into" him, and he is "into" us. When I was younger, we used to say someone was "into" something, meaning they really liked, found huge pleasure in, and were not easily swayed from their commitment to the thing or person they were "into". Perhaps this is what John has in mind here - begin so "into" each other that we don't have any desire for something else to fill our time, energies, or focus.
Genuine faith is also evident in the life which is reproduced. John put it, "He's given us life from his life, from his very own Spirit." When life is "given" there is a reproducing effect, is there not? For example, when we plant a grapefruit seed, tending it well, giving it just the right environment to grow, doesn't it produce that from which it was planted? Yep, it becomes a grapefruit tree. So, if Christ "plants" his life in us, won't what is produced in us be his life? Yep, we become "kindred" spirits! His Spirit meshes with our spirit and we take on the image of the one from which all life is produced. So, in looking upon an individual, we might do well to examine the spirit - for the spirit is the place of "intertwined" relationship with the Lord.
Most importantly, I think John hits the nail on the head when he tells us those who "proclaim" faith in Christ actually "live out" faith in Christ because they have a continual intimate relationship with him. There aren't a whole lot of gaps. This speaks of "continuity". Let me give you an example to help you get hold of this concept. If we take a piece of paper and fold it over on itself, we form a "pocket" of sorts, but both ends are open, allowing for the escape of anything we put into the "pocket". Now, get some glue and spread it evenly across the surface of the ends, pushing the paper together on the edges. What happens is that you "seal" the pocket so it can hold what we put into it.
We still have paper, folded in two, but it changed because of the "continuity" of the edges. The two became one with the use of the "glue". So, I think we often "transform" who we are by the "closeness" of the relationship we have not just on the edges of our lives, but also in what is formed in the process of "sealing up" the edges. In other words, we form a "pocket" for Christ's love to dwell. Living out faith is nothing more than being continually filled with the goodness of Christ. The two becoming one allow for the "stuff" put into our lives through relationship with Christ to actually be "contained" in our lives - giving us evidence of relationship.
Sometimes we see the "edges" of life as a little unimportant. I hope you see that even the "edges" of life are significant! Without "sealing" the edges, we might just be in "casual" contact with the one we'd do much better learning to contain! Just sayin!