John 17:19 KJV
And for their sakes I sanctify myself, that they also might be sanctified through the truth.
We generally think of sanctification as the process whereby the Christian becomes
- Less like this world and more like the Saviour,
- Less attached to this life and more consecrated to the next,
- Less subject to the sin nature and more subject to the leading of the Holy Spirit's prompting
In none of these could Jesus have needed sanctification. This leaves us wondering in what ways Christ may have sanctified Himself.
The first proposition is that He sanctified Himself in the sense of a minister and servant; having left heaven to shepherd His sheep. In this manner Christ serves as the prime example to those in ministry. We consecrate (sanctify) ourselves to the work of the ministry after the manner that Christ consecrated (sanctified) Himself for that same work. We learn the ministry by following His lead.
The second and more likely, given the context, is that Christ sanctified (consecrated or gave) Himself to die on the Cross, without which none of His disciples could have been consecrated (set apart) as God's own. Jesus sanctified Himself to become sin for us son that we might be sanctified as the righteousness of God in Him.