What is the biblical basis for in the Catholic theology of a priest being "in persona christi"?

What is the biblical basis for in the catholic theology of a priest being "*in persona christi*"? The idea that only a Priest can conduct the New Testament Passover meal that Christ told us to "do in remembrance of Him" was for all believers surely? Why is it that in Catholicism the Priest is essentially "*in persona Christi*" and is therefore the only way for a "valid" communion meal? Where in the Bible is the justification for a Priest being *in persona Christi*? (an emphasis especially on the Eucharistic sacrament please, but also interested in the theology as a whole). Thank you.