God abides in us. And since God is love, his presence in us is the perfecting or completing of his love in our love for each other. The love that you have for the children of God is a manifestation of the Spirit of God within you. The Spirit does not merely manufacture love like IBM manufactures computers or like an old man in Tarkpoima weaves a straw hat. The Spirit bears the fruit of love.
Fruit is one with the tree.
The Spirit is the love of God. Verses 14-15 seem like a break in the flow of thought. God is love, and he who abides in love abides in God, and God abides in him. So here we are back where we started. The experience of abiding in God, that is the experience of salvation, is manifested and preserved through abiding in love.