As St. John's words make clear, faith and love always run together, which means we cannot have real faith in Christ without having love for one another. Love is the fruit of faith, like apples are the fruit of an apple tree. If the tree is alive and well and drawing nutrients from the soil and energy from the sun, it produces fruit. Likewise, if faith in Christ is alive and well, drawing life from Him through His Word and Sacraments, it produces love.
God’s love was shown in this: that He sent His only Son into the world, so that we might live through Him. We did not first love God; rather, God first loved us, and He sent His Son to be the atoning sacrifice for our sins. Christ came out of love for us, while we were still loveless and unlovable. He laid down His life for us, so that we might live through Him and love through Him, and He through us.
Jesus knew His disciples. He knew what was in their hearts. He knew they were prone to arguing, to envy, to bickering over who was the greatest among them, who would get the seats of honour, who was in charge. He knew that they were opinionated men, passionate men. He knew they could be egotistical and self-centered, worried about themselves instead of each other. Jesus knew all that, and yet He loved them. He washed their feet, and He gave them a place at His table, and He said, "Love one another, as I have loved you."
And Jesus knows us. He knows what is in our hearts. Yet He loves us, bathing us in the waters of baptism and giving us a place at His table. He works in our hearts and He fills them with His love. He says to all of us as His disciples, "Love one another, as I have loved you."
It is the Lord Jesus Christ who is the actual source of His love. He is the Vine, we are the branches. Apart from Him, we can do nothing. Apart from Him, we cannot really love. Unless we are first joined to His death and His life by faith, unless we are buried with Him in baptism and are raised with Him and seated with Him in glory, unless we are in communion with Him and He with us, we will not and cannot truly love God or one another.
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Pictured: "Christ the True Vine" 16th century Greek icon