After having said "Lo Se'anun", why does the Torah repeat "Im Anei Se'aneh Oso"?
Seforno: To teach us that the prohibition is confined to where one afflicts them in order to hurt them, but not if one does so in order to chastise them and to guide them on the right path. 1
Hadar Zekenim (21): If you want to be afflicted, afflict them, for perhaps he will cry and I will hear it, and be angry...
In which case it is even a Chesed to do so (Seforno). See also Ba'al ha'Turim.
Why does the Torah use the double Lashon "Im Anei Se'aneh. "?
Mechilta #1: To teach us that Hashem will hear their cries, irrespective whether the Inuy is a major one or a minor one.
Machilta #2: To teach us that Hashem will only intervene if one transgresses twice.
See Oznayim la'Torah who explains the three double expressions ("Im Anei Se'saneh", "Tza'ok Yitz'ak" and "Shamo'a Eshma') in this Pasuk.
Why does the Torah not spell out the punishment of someone who afflicts a widow or an orphan?
Rashi: The Torah tends to issue a threat and to leave the punishment unsaid. 1
Ramban: Translating the word "Ki" to mean 'Im' (if), 2 the Torah is saying that if one afflicts a widow or an orphan, then, when they cry out to Hashem, He will answer their prayers. Moreover, whereas others in the same situation require additional Hishtadlus, Hashem will answer them as soon as they turn to Him, without any effort on their part. 3
As it does with Kayin in Bereishis, 4:15 (See Ramban's objection to both Rashi's explanation and his proof).
Which it writes twice for emphasis (Ramban).
QUESTIONS ON RASHI
Rashi writes that the Torah left the punishment unsaid. It says 'I will kill you, and your wives will be widows...!'
Riva, Rosh, Moshav Zekenim #1, Hadar Zekenim (21): That is only if the afflicted party screams to Hashem. If they do not scream, the Torah did not say what will be the punishment.
Rosh citing R. Shmuel ha'Kohen, Moshav Zekenim #2: Rashi means that the Torah did not teach the punishment for the one who screams. One who could go to Beis Din, and asks Hashem to judge, he is punished first (Bava Kama 93a). 1
Moshav Zekenim #3: Rashi means that the Torah did not teach immediately the punishment. It interrupted, and said first "if he will scream..."
Also his punishment was taught! The Gemara there learns from "Eschem" (plural) that Hashem will kill also the one who screams! (PF)