As Jesus prayed the High Priestly Prayer in John 17, his time with the disciples was winding down. There in the upper room, Jesus and the disciples had just observed the Passover, and Christ had just instituted the Lord’s Supper. Both of those observances symbolized what He was about to do.
The Passover was a celebration of God leading the children of Israel out of Egypt by delivering them from the curse of the death angel and by leading them through the Red Sea. To commemorate this event, the Israelites were commanded by scripture to sacrifice a yearling lamb, without spot or blemish, to sweep all leaven out of the home, and to eat unleavened bread and drink wine (but not in a way to get drunk).
In scripture, Egypt is a symbol of the bondage of sin. The Lamb symbolizes a sacrifice made to God to atone for sin. The blood pays the penalty for sin. The Passover celebration pictured Christ, that sacrificial Lamb that took away the sins of the world, and by so doing, led His people out of the bondage of sin.
The unleavened bread given by the Lord as He instituted the Lord’s Supper symbolized His body, and the wine symbolized the blood that redeemed us from sin. This was about to be fulfilled by Christ as He went to the cross.
This truly was a powerful moment in the life of Christ, the lives of His disciples, and truly one of the most powerful moments for all human history. The symbols of our redemption intersecting with our moment of redemption, coupled with the imminent separation of Christ from His beloved disciples, drove our Lord to prayer, and thus we have recorded in the Gospel of John the High Priestly Prayer of Christ.
In John 17:17-19, Jesus prays for God to sanctify His disciples through truth, noting that God’s word is truth, and declares that He is sending the disciples into the world. From this, we learn about the sanctification of the disciples of Christ, the mission of the disciples of Christ, and the sanctification of Christ Himself.

In John 17:17, Jesus prayed, “Sanctify them through thy truth, thy word is truth.”
The word “sanctify” was translated from the Greek hagiason, which in this case means to purify internally by the reformation of the soul.
In this prayer, Jesus was praying that God would transform the disciples from the inside out through His truth, which is written in His word, the Bible. Indeed, the Bible has transformative power, especially when one completely grasps the central message of the scriptures.
The Gospel, how Jesus died for our sins, according to the scriptures, was buried, and rose again the third day is the central theme of the Bible. Scripture fills out this message by introducing us to God through the creation in Genesis 1, demonstrating Him as the source of our lives in Genesis 2, depicting His formulation of our redemption in the immediate aftermath of our sin in Genesis 3:15, teaching that He demands sacrifice by faith and not empty works in Genesis 4, showing His gracious rescue of His people in Genesis 6-8, His ultimate sacrifice in the story of Abraham and Isaac, His redemption of His people from the bondage of sin in Exodus through Deuteronomy, and His provision for the faith-filled life in the book of Joshua.
Psalms declares His glory. Song of Solomon declares His passion. Isaiah declares His salvation. The four Gospels the events of the life of Christ that purchased our redemption, and Revelation foretells God’s final victory and our final deliverance.
These scriptures depict a God who gave us life so that we could have fellowship with Him, and Him companionship with us. Instead, we rejected Him and tried to overthrow His presence from our lives. Instead of accepting this rejection and allowing us to die the death that comes from cutting ourselves off from the source of life, He (through Christ) died that death on our behalf so we could be reconciled, endowed with eternal life, and reunited with Him in His Kingdom.
The deeper we understand this truth, the deeper we understand the Gospel, the more our souls are transformed into the people God intended on us being. The more fully we understand the Gospel, the more sanctified we are.
After praying for our sanctification, Christ then told why He wanted us sanctified.

Jesus told the Father that, as He was sent into the world, He was sending His disciples into the world.
In Matthew 28:19-20, Mark 16:15 and Acts 1:8, we find that Christ sent His disciples into the world to preach and bear witness of the Gospel. Like His disciples, we are called to go into all the world preaching the Gospel to all who will listen, and baptizing those who believe, following up with good doctrinal teaching.
That is the reason we live as followers of Christ, and the reason our church exists.
Finally, Christ said that He sanctified Himself so that the disciples could be sanctified. In this sense, Christ was set apart, consecrated, and holy, as He prepared to go to the cross to redeem us.
These few verses in the larger High Priestly Prayer of Christ should remind us of the transformation God has worked in our lives, and motivate us to carry His Gospel to a lost and dying world.