Eusebius referring to his own day wrote:
We [sank] into negligence and sloth, One in being and reviling another in different ways, and we were almost, as it were, on the point of taking up arms against each other, and where is sailing each other with words as with darts and Spears, prelates inveighing against prelates, and people rising up against people, and hypocrisy and dissimulation had arisen to the greatest height of malignity; … we added one wickedness in misery to another. But some that appeared to be our pastors, deserting the law of piety, were inflamed against each other with mutual strides, only accumulating quarrels and threats, rivalship, hostility and hatred to each other. (Eusebius, ecclesiastical history, 8:318)
Tertullian observed “The gospel was wrong we preached; men wrongly believed; so many thousands were wrongly baptized… so many priestly functions, so many ministries were wrongly executed.” (The Ante-Nicene Fathers, 3:256)
Adolf von Harnack commented on the much-changed Christianity after a century of compromise and worldly assimilation:
If we place ourselves about the year 200, about 100 or 120 years after the apostolic age… what kind of spectacle does the Christian religion offer?.. The living faith seems to be transformed into a creed… devotion to Christ, into Christology… prophecy, into technical exegesis and theological learning; The ministers of the Spirit, into clerics… miracles and miraculous cures disappear altogether… The “Spirit” becomes law and compulsion… this enormous transformation took place within 120 years. (Von Harnack, What is Christianity? 192-93)"
Cyril of Jerusalem stated…
Thus wrote Paul, and now is the falling away. For men have fallen away from the right faith; and some preach the identity of the Son with the Father, and others dare say that Christ was brought into being out of nothing. And formally the heretics were manifest; but now the Church is filled with heretics in disguise. For men have fallen away from the truth, and have itching ears. It is a plausible discourse? All listen to it gladly. Is it a word of correction? All turn away from it. Most have departed from right words, and rather choose the evil, than desire the good. This therefore is the falling away, and the enemy is soon to be looked for… (Cyril of Jerusalem, Catechetical Lecture 15:9, in NPNF Series 2, 7:106-107)
Justin Martyr stated…
Just as there were false prophets contemporaneous with your holy prophets, so are there now many false teachers amongst us, of whom our Lord forewarned us to beware; so that in no respect are we deficient, since we know that He foreknew all that would happen to us after His resurrection from the dead and ascension to heaven. For He said we would be put to death, and hatred for His name’s sake; and that many false prophets and false Christ’s would appear in His name, and deceive many: and so has it come about. For many have taught godless, blasphemous, and unholy doctrines forging them in His name. (Justin, Dialogue with Trypho 82, in Ante-Nicene Fathers, 1:240)
I hope this helps…