I would have thought that was "elementary my dear Watson"

Who wants to know the truth? Me please !
How can we ascertain it? Seek knowledge, and be single-minded, regardless of the consequences.
Can we be certain that we believe correctly? No .. there is no such thing .. knowledge of God is infinite.
Are there basic things we should understand?
Yes .. Jesus, peace be with him, confirmed the shema. He did NOT say in the NT that it had been replaced.
"In the name of the Father, and of the Son, and of the Holy Spirit" does not
explicitly teach
a "blessed trinity". If it was important truth,
BE SURE, that Jesus would have been reported to have said so !
The Gospel of Truth teaches us that the Knowledge of the Father is the most important thing.
The Father is God.