17:17 “Sanctify them in the truth; your word is truth” (ἁγίασον αὐτοὺς ἐν τῇ ἀληθείᾳ· ὁ λόγος ὁ σὸς ἀλήθειά ἐστιν). Jesus now moves toward the conclusion of his prayer for the disciples by consecrating them to the mission of God. First, Jesus prays, “Sanctify them in the truth” (ἁγίασον αὐτοὺς ἐν τῇ ἀληθείᾳ). The verb “sanctify” (ἁγίασον) can mean “to separate, make holy,” but in this context refers to the act of consecrating or dedicating a person for a holy task. The same term was used in 10:36 where we translated it as “set apart” (ἡγίασεν) to refer to God’s consecration and dedication of Jesus for his mission to the world. As v. 18 is about to explain, the disciples are consecrated here and “set apart” for a related purpose, for God’s (continuing) mission to the world.

It is fitting that the disciples are to be sanctified “in the truth” (ἐν τῇ ἀληθείᾳ). By this Jesus requests that the Father immerse the disciples in the revelation of himself in the Son, sanctifying them by sending the Paraclete to them to guide them into all truth (15:13). The disciples are set apart not by their own sanctity or holiness but by that given to them by God through Jesus Christ (see v. 19). That is why Jesus then clarifies what the truth is: “Your word is truth” (ὁ λόγος ὁ σὸς ἀλήθειά ἐστιν). “Word” here probably means more than the written Scriptures (cf. 10:35). It refers to the message from the Father in and of the person and work of Jesus Christ, who sends “the Spirit of truth” (15:26) and is “the truth” (14:16), which he gave to the disciples and they have “received,” “understood,” and “kept” (see vv. 6, 8). Ultimately this is the promised fulfillment of what was announced in the prologue regarding the provision through Christ of “grace and truth” (1:17) and is even the fulfillment of what was announced in the OT.

 Edward W. Klink III, John, ed. Clinton E. Arnold, Zondervan Exegetical Commentary on the New Testament (Grand Rapids, MI: Zondervan, 2016), 721–722.