Jesus prayed - For their sake I sanctify myself

Today I'd like to share a little bit from the book "Our Lord Prays for His Own" by Marcus Rainsford. In this section which I am about to quote, the author is discussing Jesus' prayer for His own in John 17. The phrase under consideration is "I sanctify myself." Usually the idea of sanctification is that of "making holy." But Jesus was already holy. What did he mean by this phrase?

Here is what the author writes (I'm modernizing some phrases and picking and choosing from the text on pages 330 and 331):

What does He mean? He was "The Holy One of God...Holiness unto the Lord...the Most Holy"; it is utterly inconceivable that He could become more holy or more sanctified than He was, yet He says, "I sanctify myself."

The meaning here evidently is, I dedicate, I consecrate, I set apart My whole self, --My Person, Godhead and Manhood, Soul and Body. I consecrate all my offices--if I be a Priest, if I be a Prophet, if I be a King-- I set them apart, I wholly dedicate and consecrate all My fullness of grace and glory, all My righteousness, all My interest, My very existence, I sanctify for the purpose and object for which I plead.

I lay down all upon the altar of divine and unchangeable love that I may be all, do all, suffer all, merit all My people need, and, that I may pay all My people owe."

Oh! what did He hold back? Nothing! His was a complete surrender; it was an absolute devoting of Himself, all that He was as Son of God, all that He was as Son of Man, all that He was as Mediator, all His fullness, and all His service, His time, His care, His thought, His very life itself He consecrated and set apart, that He might be the sanctification of His people.

The blood of Christ has a double efficacy: it is the atonement for sin, and it is the sanctification of the sinner on whose heart it is sprinkled. "We are justified by his blood (Romans 5:9) and we are sanctified by the blood (Hebrews 13:12). This one offering of Himself includes sin-offering, burnt-offering, meat-offering, peace-offering, all in one. His blood cleanses "from all sin," both from the guilt of sin, and from the filth of sin, from every kind and degree of sin, and everything contained in sin, its pollution, its demerit, and its consequences; where the blood of the Lamb is applied by faith the Holy Spirit descends and dwells there forever.