John 17:17-19 (ESV Strong’s Bible)
” 17 Sanctify them in the truth; your word is truth.
The word sanctify means to purify or to set apart or to make holy. Jesus here, is asking God to set the disciples apart and make them holy by His word. Jesus said in John 15:3 that the disciples were clean because of the word that he spoke to them. Paul said in 2 Thes 2:13 that we must be always thankful that God chose us to be saved through the sanctification by the Spirit and belief in truth. Peter says in 1 Peter 1:22 that our souls are purified by the our obedience to the truth.
Therefore Jesus is asking God to make the disciples Holy, through His word that they have recieved and believed. It is the word of God that makes us Holy. Spending time studying the word of God will produce holiness in us.
18 As you sent me into the world, so I have sent them into the world.
Just as God sent Jesus to the world, Jesus is now sending His disciples to the world. Indeed in John 20:21, Jesus did sent them out. In this verse, Jesus is already looking forward to the John 20:21 act which has not happened yet.
19 And for their sake I consecrate myself, that they also may be sanctified in truth.”
They word consecrate means to make one clean, pure, holy, to set one self apart. Why would Jesus want to make Himslef holy, was He not holy before? Definitely No. Jesus is God reincarnate. He is obviously holy. Jesus has also up to that point, have lived a Holy life that only He can do. What Jesus is saying here is that He is going to offer Himslef as a Holy Sacrifice so that through that, the disciples can be made holy. Tit 2:14, Paul says Jesus gave Himslef for us, to redeem us from lawlessness and to purify for Himslef a people for His own possession. 1 Cor 6:11, Paul says we were sanctified in Jesus’s name. Heb 10:10, the writer says that we will be sanctified through the offering of the body of Jesus Christ once and for all. So, clearly here, Jesus is reffering to making himself a holy sacrifice so that through His death on the cross, those who beleive may be made holy. It is also important to note here that we will be made Holy in Truth. Again it goes back to spending time and studying the word of God and through faith as well, that we be made Holy.