On the need for confession

Cyprian of Carthage
"He [Paul] threatens, moreover, the stubborn and forward, and denounces them, saying, ‘Whosoever eats the bread or drinks the cup of the Lord unworthily, is guilty of the body and blood of the Lord’ [1 Cor. 11:27]. All these warnings being scorned and contemned—[lapsed Christians will often take Communion] before their sin is expiated, before confession has been made of heir crime, before their conscience has been purged by sacrifice and by the hand of the priest, before the offense of an angry and threatening Lord has been appeased, [and so] violence is done to his body and blood; and they sin now against their Lord more with their hand and mouth than when they denied their Lord" (The Lapsed 15–16 [A.D. 251]).

The Didache
"Assemble on the Lord’s day, and break bread and offer the Eucharist; but first make confession of your faults, so that your sacrifice may be a pure one. Anyone who has a difference with his fellow is not to take part with you until he has been reconciled, so as to avoid any profanation of your sacrifice [Matt. 5:23–24]. For this is the offering of which the Lord has said, ‘Everywhere and always bring me a sacrifice that is undefiled, for I am a great king, says the Lord, and my name is the wonder of nations’ [Mal. 1:11, 14]" (Didache 14 [A.D. 70]).

Who can offer the Sacrifice

Council of Nicaea I
"It has come to the knowledge of the holy and great synod that, in some districts and cities, the deacons administer the Eucharist to the presbyters [i.e., priests], whereas neither canon nor custom permits that they who have no right to offer [the Eucharistic sacrifice] should give the Body of Christ to them that do offer [it]" (Canon 18 [A.D. 325]).

The Priest stands in the place of Jesus

Cyprian of Carthage
"If Christ Jesus, our Lord and God, is himself the high priest of God the Father; and if he offered himself as a sacrifice to the Father; and if he commanded that this be done in commemoration of himself, then certainly the priest, who imitates that which Christ did, truly functions in place of Christ" (Letters 63:14 [A.D. 253]).

Ambrose of Milan
"We saw the prince of priests coming to us, we saw and heard him offering his blood for us. We follow, inasmuch as we are able, being priests, and we offer the sacrifice on behalf of the people. Even if we are of but little merit, still, in the sacrifice, we are honorable. Even if Christ is not now seen as the one who offers the sacrifice, nevertheless it is he himself that is offered in sacrifice here on Earth when the body of Christ is offered. Indeed, to offer himself he is made visible in us, he whose word makes holy the sacrifice that is offered" (Commentaries on Twelve Psalms of David 38:25 [A.D. 389]).