It’s the old maxim, whether it’s church history or other history: those who refuse to study history are doomed to repeat it.
Virtually every heresy we face today is a rehash of some heresy that the church has already had to deal with in history. God has preserved His church through all the centuries, and we hope that by now we’ve learned something.
Why did Luke write the book of Acts? He wrote his Gospel, but he also wrote the early history of the Christian church, which was very important for the church to understand its origins, its mission, and its doctrine.