The apostle Paul foretold that the true Christianity of the first century would apostatize. This began in the early centuries after the death of the apostles and has continued down to our day.
"Let no one lead you astray in any way, because it will not come unless the apostasy comes first and the man of lawlessness gets revealed, the son of destruction."—2 Thessalonians 2:3
"However, the inspired word clearly says that in later times some will fall away from the faith, paying attention to misleading inspired statements and teachings of demons."—1 Timothy 4:1
"For there will be a period of time when they will not put up with the wholesome teaching, but according to their own desires, they will surround themselves with teachers to have their ears tickled."—2 Timothy 4:3