The Early Church Fathers on various topics: This was a 3700 hour project which included going through 22896 pages of the 38 volume set called Ante Nicene, Nicene, Post Nicene Fathers. I compiled 255 pages of quotes showing that the Early Church was always and completely Catholic. All of these quotes can be verified and found from the source which is free online.
Tertullian On Modesty ch 21 [160-240 AD]
"Discipline governs a man, power sets a seal upon him; apart from the fact that power is the Spirit, but the Spirit is God. What, moreover, used [the Spirit] to teach? That there must be no communicating with the works of darkness. Observe what he bids. Who, moreover, was able to forgive sins? This is his alone prerogative: for 'who remits sins but God alone?' and, of course, [who but he can remit] mortal sins, such as have been committed against himself and against his temple?"
Origen Commentary on Matthew book 14 ch 10 (185-254)
But observe here that every great sin is a loss of the talents of the master of the house, and such sins are committed by fornicators, adulterers, abusers of themselves with men, effeminate, idolaters, murderers
Cyprian of Carthage epistle 74.17 (200-270 ad)
by the sacrament of baptism, the filth of the old man is washed away by them, that they pardon the former mortal sins, that they make sons of God by heavenly regeneration, and renew to eternal life by the sanctification of the divine layer
John Chrysostom Homily 75 on Matthews Gospel (347-407 ad)
For not for all sins are there the same punishments, but many and diverse, according to the times, according to the persons, according to their rank, according to their understanding, according to other things besides. And that what I say may be more clear, let one sin be set forth, fornication; and mark how many different punishments I find not from myself, but from the divine Scriptures. Did any one commit fornication before the law, he is differently punished; and this Paul showeth, "For as many as have sinned without law, shall also perish without law."Did any one commit fornication after the law? He shall suffer more grievous things. "For as many as have sinned in the law shall be judged by the law."Did any one commit fornication being a priest, he receives from his dignity a very great addition to his punishment.
Jerome Against Jovinianus book 2 par 30 [347-420 AD]
Some offences are light, some heavy. It is one thing to owe ten thousand talents, another to owe a farthing. We shall have to give account of the idle word no less than of adultery; but it is not the same thing to be put to the blush, and to be put upon the rack, to grow red in the face and to ensure lasting torment. Do you think I am merely expressing my own views? Hear what the Apostle John says: him ask, and he shall give him life, even to him that sinneth not unto death. But he that hath sinned unto death, who shall pray for him? "You observe that if we entreat for smaller offences, we obtain pardon: if for greater ones, it is difficult to obtain our request: and that there is a great difference between sins.
John Chrysostom Homily 25 on Romans (347-407 ad)
Well then, shall the whoremonger, and the adulterer, and the man who hath done evils unnumbered, enjoy the same advantages with the man who has exhibited soberness and holiness, and Paul is to stand with Nero, or rather even the devil with Paul? For if there be no hell and yet there will be a Resurrection of all, then the wicked will attain to the same good things!
John Cassian Conference 17 ch 18 (360-435 ad)
And in the same way we hold that no lie can be employed by any one, I will not say rightly, but not even venially,
Augustine of Hippo City of God Book XXI ch 13 [354-430 AD]
"But those who do not belong to the number of the predestined . . . are judged most justly according to their deserts. For either they lie under sin which they contracted originally by their generation and go forth [from this life] with that hereditary debt which was not forgiven by regeneration [baptism], or [if it was forgiven by regeneration] they have added others besides through free choice: choice, I say, free; but not freed. . . . Or they receive God's grace, but they are temporal and do not persevere; they abandon it and are abandoned. For by free will, since they have not received the gift of perseverance, they are sent away in God's just and hidden judgment" (ibid.,13).
Augustine Disposition day 2 Against Fortunatus the Manichean par 21 (354-430 ad)
I say it is not sin, if it be not committed by one's own will