We know how the Apostles interpreted the scripture because we have the earliest Catechism of the Apostles as well as the understanding of the earliest Christians.
What is new and novel is the protestant rejection of this interpretation.
"In church confess your sins, and do not come to your prayer with a guilt conscience. Such is the Way of Life...On the Lord's own day,assemble in common to break bread and offer thanks; but first confess your sins,so that your sacrifice may be pure" Didache (The Writings of the Apostles),4:14,14:1(A.D.70),in ACW,6:18,23
Father who knowest the hearts of all grant upon this Thy servant whom Thou hast chosen for the episcopate to feed Thy holy flock and serve as Thine high priest,that he may minister blamelessly by night and day,that he may unceasingly behold and propriate Thy countenance and offer to Thee the gifts of Thy holy Church. And that by the high priestly Spirit he may have authority to forgive sins..." Hippolytus,Apostolic Tradition,3(A.D. 215),in AT,4-5
"In addition to these there is also a seventh, albeit hard and laborious: the remission of sins through penance...when he does not shrink from declaring his sin to a priest of the Lord" Origen,Homilies on Leviticus,2:4(A.D. 248),in JUR,I:207
I entreat you, beloved brethren, that each one should confess his own sin, while he who has sinned is still in this world, while his confession may be received, while the satisfaction and remission made by the priests are pleasing to the Lord?" Cyprian,To the Lapsed,28-29(A.D. 251),in ANF,IV:445
"For although in smaller sins sinners may do penance for a set time, and according to the rules of discipline come to public confession, and by imposition of the hand of the bishop and clergy receive the right of communion: now with their time still unfulfilled, while persecution is still raging, while the peace of the Church itself is not vet restored, they are admitted to communion, and their name is presented; and while the penitence is not yet performed, confession is not yet made, the hands Of the bishop and clergy are not yet laid upon them, the eucharist is given to them; although it is written, 'Whosoever shall eat the bread and drink the cup of the Lord unworthily, shall be guilty of the body and blood of the Lord.' " Cyprian,To the Clergy,9(16):2 (A.D. 250),in ANF,IV:290
"It is necessary to confess our sins to those whom the dispensation of God's mysteries is entrusted." Basil,Rule Briefly Treated,288(A.D. 374),in JUR,II:26