Was Jesus The Lamb of God or the High Priest (that offers the lamb as a sacriffice)? Was Jesus The Lamb of God or the High Priest (whom offers the lamb as a sacriffice)?
John the baptist said &quot; Behold the Lamb of God, which taketh away the sin of the world&quot; John 1:19
And in Hebrews 4:14 it is written &quot;Seeing then that we have a great high priest, that is passed into the heavens, Jesus the Son of God&quot;.
He was both, but offered Himself, His own body as the perfect sacrifice. The book of Hebrews goes into great details. If you have a little time, read an overview commentary of Hebrews; if you have a medium amount of time, read a study Bible or commentary that goes verse by verse; If you have a lot of time, I strongly recommend the Naked Bible podcast by Dr. Michael Heiser, wherein he breaks down the book in great detail using a lot of knowledge of 1st Century Middle Eastern cultural background, but explains things in laymen's terms. He covers the book of Hebrews over several episodes. If you wish, you could focus on Hebrews 10, which deals specifically with the sacrifice. 

Starting from verse 4 (I'm using the NLT):
"4 For it is not possible for the blood of bulls and goats to take away sins. 5 That is why, when Christ came into the world, he said to God,

“You did not want animal sacrifices or sin offerings.
    But you have given me a body to offer.
6 You were not pleased with burnt offerings
    or other offerings for sin.
7 Then I said, ‘Look, I have come to do your will, O God—
    as is written about me in the Scriptures.’”

8 First, Christ said, “You did not want animal sacrifices or sin offerings or burnt offerings or other offerings for sin, nor were you pleased with them” (though they are required by the law of Moses). 9 Then he said, “Look, I have come to do your will.” He cancels the first covenant in order to put the second into effect. 10 For God’s will was for us to be made holy by the sacrifice of the body of Jesus Christ, once for all time.

11 Under the old covenant, the priest stands and ministers before the altar day after day, offering the same sacrifices again and again, which can never take away sins. 12 But our High Priest offered himself to God as a single sacrifice for sins, good for all time. Then he sat down in the place of honor at God’s right hand. 13 There he waits until his enemies are humbled and made a footstool under his feet. 14 For by that one offering he forever made perfect those who are being made holy.