The ordination in Leviticus 8 is closely related to "it is finished" and does shed light on the interpretation of the fulfillment of the law.
The Hebrew word Strong’s H4390 - מלא (ml’) is the same as 04394 מלא millu’ (remembering that modern vowels were not added until about 600 AD.)
The sense of setting a stone in place is similar to setting a priest in place, and it is the same as locking the law into place. Locking the law can best be understood as giving the law it's permanent context.
For instance, there is no moral aspect about eating unclean animals; if there were, God would not have changed his mind on it. It was a teaching aid; a kind of dinner theater, to prepare Israel for a deeper understanding of God (whom no man has seen) through the words, works, life, death, and resurrection of the Son.
The clean animal ruminated and had a split hoof. Eating is a metaphor for learning, so a clean animal is one who ruminates on the word of God, and it produces a holy (separate) life (walk). One type of unclean animal was like the Pharisee who had a form of holiness (split hoof) but it was not based in the word, but in his own estimation of his worth (did not ruminate). The other unclean animal was like the scribe who knew the scripture well (ruminated) but it did not produce a holy life (split hoof).
Since we now see the purpose of the law, it is no longer necessary to practice it. While we eat the abomination called a lobster we are reminded that it represents the one who lives in the flesh (earthly bottom of the sea) and snatches God's children (those living in the water/word and wearing the armor of God -scales) from the word/water and drags them into the flesh (the bottom) to devour them. This is the person who causes a little one to sin.
The law is set into it's final context.
The ordination of priests was the similar to the cermony for cleansing a leper. The law of the leper has been set into it's final context.
Leprosy represented sin. The leper shaved his head (The Father separated from Jesus at the cross). He covered his lip, a symbol of not having your prayer answered (Jesus prayed "Remove this cup"). He tore his clothes/works (Jesus shredded his works and died alone, all his work to that point; facing temptation without sin, was apparently fruitless at that time). He was set outside the camp (the place of the cross). And when the leper was fully covered with leprosy, he was declared clean (When Jesus fully bore our sin and rose from the dead, he was righteous and holy).
The ceremony of the leper represented the ordination of Jesus as our high priest in his resurrection.
Each and every law has a shadow of "the kingdom of God" called the "good things coming" in Heb 10.1
As for keeping the law: If one loves... puts God and others first... all the literal law is kept in it's spiritual purpose. One does not kill, covet, etc. if he loves.
To understand fulfilling the prophets, one must first see the embedded prophecy in the literal history of Israel. This is the topic of sensus plenior. See elsewhere the birth of Christ hidden in Genesis 38.