You could not have done that in 325. It was all up in the air.
And up until that time, Christians simply put their faith in Jesus for salvation and were saved without having all their doctrine and dogma defined for them.
People can have all their theological i's dotted and T's crossed and still not know Jesus.
And people can do nothing more than that Jesus died for them and they need Him to forgive them and still be saved.
When the Philippian jailer asked Paul what he must do to be saved, Paul replied with a simple, "Believe in the Lord Jesus, and you will be saved".
It's only the religious that demand that people have their doctrine down before they can be saved.
God is perfectly capable of correcting any erroneous doctrine someone may have about Him after they are saved.
What was going on in Acts 15?