1)
What is the grammatical form of "Hatzel"?
1.
R. Yonah: It is Makor (like an infinitive)
2)
What does our verse teach?
1.
Rashi: If you will slacken from saving those taken to die, also when they are about to be killed - then, I said that your strength will be weak (10).
2.
R. Yonah: This additionally explains "Hisrapisa b'Yom Tzarah" (10). The coming verse "Hen Lo Yadanu Zeh" shows that "Hisrapisa..." refers also to slackening in thought.