On the first commandment: How to command to believe in oneself

Hello.
I just wanted to clarify what I wrote in the email.

This is what you told me:
There are two different suggestions here.
1. To make knowledge solid means to examine and deepen, which is roughly what I said in the lesson. But still, if my conclusion is that there is no God, it cannot be said that I have abrogated a positive commandment. According to this, as I answered a question asked me in the lesson, rabbis who say not to examine faith intellectually are inciting the abrogation of a positive commandment.
2. You suggest that this is just a definition and not a mitzvah. But I said in class that this is what I also thought (that it is a definitional mitzvah, like the Rambam does in verse 6), and Pixler corrected me for my mistake, because the Rambam listed this as part of the sixty eternal mitzvot that a person always fulfills. It is impossible to fulfill a definitional mitzvah.

And the clarification:

1) I don't know if it's exactly the same thing. According to you, the problem is: How can a commandment check whether it actually exists?
What I wanted to say is that there is a difference between knowing that there was a Mount Sinai event and that there is a legitimate mitzvah and between (investigating in order to) know that this mitzvah is, as the Maimonides says, an ale and a sabah and it applies to all who are present.
2) My suggestion is regarding the Thirteen Principles. For example, someone who does not believe in the coming of the Messiah is an Epicurus. The Principles are not commandments.