What is the meaning of their saying "al-sadr" and "the necessity of al-sadr"?

The Shaykh : The difference between them is that the necessity of the chest has the priority in itself; the subject itself has the priority. Did you understand? "Or was": meaning the predicate is attributed to a subject with the letter lam of inception, for example: "Lazaid qaim" (Zaid is standing). Now, the subject itself does not have the priority. Who has the priority?
The student: The interrogative.

The Shaykh : As for: "Who is there to help me", "who" itself has the priority. So the difference between them is: in the first case, the subject does not have the priority, but the priority belongs to what it is joined to, which is the lam. Here, the priority belongs to the subject. This is the difference. Is it clear?
The student: Yes.

The Shaykh : Okay, do we have a recitation or not?
The student: No, no, a new lesson.

The Shaykh : Huh? A new lesson, we heard, Khalid, a new lesson! -Benefit, benefit, Muhammad- .
The student: I am busy, Shaykh.

The Shaykh : Busy?! Meaning more important than the Alfiyyah?
The student: Yes.

The Shaykh : Alright, alright, may Allah heal him and keep him safe.
The reader: In the name of Allah, the Most Gracious, the Most Merciful.
The author said - (may Allah have mercy on him) - :
"And the original rule for predicates is that they are delayed *** And they permitted advancing them when there is no harm" .

The Shaykh : Why? And "I have a dirham with me," you were not present yesterday?
The reader: I was present.

The Shaykh : What do you say?! This is explained and finished!
The reader: The grammar is correct.

The Shaykh : No, it is finished.