1 John makes it clear that you need to understand the truth in order to be saved. In Acts, we see that a person needs to believe in his heart and confess with his mouth. Clearly, when Luke was writing that someone needed to believe in his heart, he is referring to something specific and not some generality that can vary.
Historically, that "something" has been outlined in the various creeds of the faith. That Jesus was born of the Virgin Mary, was both God and man, lived a perfect life, was crucified, died and on the third day rose again. That he suffered the righteous wrath of God in our place to pay the sin debt we owe God and that he imputes his righteousness to us.
Those are the basic tenets of the Christian faith and are call primary doctrines. In other words, they are non-negotiable. There are other doctrines, called secondary doctrines, such as infant baptism, gifts of the Spirit, etc, where Christians can hold different views and still be genuine Christians.
All good and true ... but that's really just a list meant to define the limits of an organized religion. They are not the means of salvation.
Jesus was not concerned with checking off the boxes. In fact, he most strongly opposed the folks who demanded it.
Perhaps salvation is much simpler matter than organized religion would like it to be.
Remember: the thief on the cross was saved despite his ignorance of those doctrines. The Samaritan woman at the well, likewise.
It was nothing more or less than the way they responded to Jesus that saved them.
Think about it....