The Lord Commanded Us To persevere and practice This Sacrament
He commanded that this sacrament must be perpetually conducted in commemoration of Him when He said;
“Do this in remembrance of Me”.
Hence, we would be breaking His commandment, if we do not continue to practice this Sacrament.
(1 Cor 11:25) In the same manner He also took the cup after supper, saying, "This cup is the new covenant in My blood. This do, as often as you drink it, in remembrance of Me."
(Luke 22:19) And He took bread, gave thanks and broke it, and gave it to them, saying, "This is My body which is given for you; do this in remembrance of Me."
 “Do This” Is A Special Command
It is obvious that the Lord has placed a special emphasis on conducting this Sacrament through His Words, as we have discussed this issue before here on st-takla.org in other sections. This necessitates a special grade of people (the priests) to carry out this command.
So the Holy Spirit through the invocation of the priest should carry out the transubstantiation.