John 15:3

Already ye are clean because of the word which I have spoken unto you.

Christ here intimates that the apostles do not at the moment need "pruning," having already been pruned enough by the devastating teachings and revelations of that entire evening. Their pride, secularism, trust of themselves, and their vain ambitions had all been swept away in the knowledge of Judas' treachery, Peter's forthcoming denial, and the Lord's impending death, the latter being a fact that their minds could no longer avoid. However, the idea persists that these words were spoken prophetically, the present tense being used for the future; because, actually, much pruning remained for the beloved Twelve.

Because of the word ... The instrument of cleansing from sin is the word of God. Some have supposed the Holy Spirit to be the cleansing agent in redemption; but this is not true, if by "agent" is meant the means of cleansing. The Spirit is sent into men's hearts not to make them sons of God, or to cleanse them, but because they are already so (Galatians 4:6). "The sword of the Spirit ... is the word of God" (Ephesians 6:17); therefore, the word of God is the means and the Holy Spirit is the applicator or wielder of the means of cleansing from sin. What was true of the Twelve is true of all who are ever saved. It is "because of the word" of God.