Humility is to …/Humility is that …/ To be humble, understanding …

[Odessa Dawn]

Humility is to understand who you are and what you are capable of.
Humility is that understanding who you are and what you are capable of.

To be humble, is to understand who you are and what you are capable of.

Are they free from grammatical mistakes, please?

 

[MikeNewYork]

The first is grammatical, but not very natural.
The second would be fine without "that".
The third would be fine without the comma.

 

[Matthew Wai]

How about 'Humility is that you understand who you are and what you are capable of'?
Not a teacher.

 

[MikeNewYork]

Not terribly natural for me.

 

[tedmc]

How is that you can equate 'humility' which is a noun to 'understand' which is a verb?

 

[MikeNewYork]

"To understand" is an infinitive, which is also a noun. "Understanding is a gerund, which is also a noun.

 

[Matthew Wai]

How about 'Humility is the understanding of who you are and what you are capable of'?
Not a teacher.

How is that you can equate 'humility' which is a noun to 'understand' which is a verb?

I think you might have come across something like 'the plan is to +infinitive'.