11 Beloved, if God so loved us, we also ought to love one another. 12 No one has seen God at any time; if we love one another, God abides in us, and His love is perfected in us. 13 By this we know that we abide in Him and He in us, because He has given us of His Spirit. 14 We have seen and testify that the Father has sent the Son to be the Savior of the world. 15 Whoever confesses that Jesus is the Son of God, God abides in him, and he in God. 16 We have come to know and have believed the love which God has for us. God is love, and the one who abides in love abides in God, and God abides in him.
This passage reminds me of the first part of John 15 (NASB), which is one of my favorite passages because we memorized it in college:
4 Abide in Me, and I in you. As the branch cannot bear fruit of itself unless it abides in the vine, so neither can you unless you abide in Me. 5 I am the vine, you are the branches; he who abides in Me and I in him, he bears much fruit, for apart from Me you can do nothing. 6 If anyone does not abide in Me, he is thrown away as a branch and dries up; and they gather them, and cast them into the fire and they are burned. 7 If you abide in Me, and My words abide in you, ask whatever you wish, and it will be done for you. 8 My Father is glorified by this, that you bear much fruit, and so prove to be My disciples. 9 Just as the Father has loved Me, I have also loved you; abide in My love. 10 If you keep My commandments, you will abide in My love; just as I have kept My Father's commandments and abide in His love.