It was not necessary i dont believe, but was done for the sake of the Disciples & those who would look upon this later on. When Jesus mentions an OT passage like, “My God, my God, why has thou forsaken me?”, the people immediately think of Psalm 22 & remember that this Psalm has a happy joyous fulfillment, but only after the suffering servant goes through what must take place. And when He breathes on them, telling them that the authority & mission His father gave Him is now been passed onto them. They would also immediately hearken back to Genesis & recognize that they are receiving a new spirit, they are a new creation. Christ does this a lot, like in Matthew 16 → Isaiah 22. But not only by His word’s but His deeds, like the cruzifiction which hearkens back to Abraham & Isaac. And here God in Christ is instituting the Church, no longer is it just Israel who are the people of God but all the nations. And so He breathes on them reminding them of His new creation in Genesis, when He breathed on them. And He gave Adam a mission also, to to till and to guard it which are priestly duties. The only other time these instructions come up in OT scripture is when Aaron & the Levitical priesthood receive their duties
[Genesis 2:4-8]
“These are the generations of the heavens and the earth when they were created. In the day that the Lord God made the earth and the heavens, when no plant of the field was yet in the earth and no herb of the field had yet sprung up—for the Lord God had not caused it to rain upon the earth, and there was no man to till the ground; but a mist went up from the earth and watered the whole face of the ground— then the Lord God formed man of dust from the ground, and breathed into his nostrils the breath of life; and man became a living being.”