In the fourth Gospel Jesus often speaks in theological terms of interconnection. In John 15 he speaks of it as “witness of the Spirit.” He explains it with the simile of the vine and the branches. Jesus is the true vine. The Father is the vine grower (v. 1) who removes the branches that do not bear fruit, and prunes (literally “cleanses,” kathairei) the branches that bear fruit.
The verb “ to clean” also appears in the fourth Gospel during the washing of the feet (John 13:10), when Jesus says to his disciples: “One who has bathed does not need to wash, except for their feet, but is entirely clean (katharos). And you are clean, though not all of you.” Since he knew who was to betray him, he said “not all of you are clean.”
The pruning of the branch that bears fruit so that it will bear more fruit (v. 2) is an example and an explanation of the baptismal meaning of the washing of the feet, according to the explanation that Jesus gives to Peter in John 13:8: “Unless I wash you, you have no share with me.” The Father, who is the vine grower, “cleans” the disciples of Jesus by means of his passion, unites them to his passion and death, so that by the gift of his life and the Holy Spirit they may be united to him and to his resurrection.
The disciples, cleansed by the word that Jesus announced, have access to a salvific dialogue, participate in the communion of Jesus with the love of the Father, and are invited to abide in him. Otherwise they are like a branch detached from the vine, which serves no purpose.