not by chance

We end off Eichah with the pesukim

 לָ֤מָּה לָנֶ֙צַח֙ תִּשְׁכָּחֵ֔נוּ תַּֽעַזְבֵ֖נוּ לְאֹ֥רֶךְ יָמִֽים

הֲשִׁיבֵ֨נוּ הֹ׳  אֵלֶ֙יךָ֙ וְֽנָשׁ֔וּבָה חַדֵּ֥שׁ יָמֵ֖ינוּ כְּקֶֽדֶם

כִּ֚י אִם־מָאֹ֣ס מְאַסְתָּ֔נוּ קָצַ֥פְתָּ עָלֵ֖ינוּ עַד־מְאֹֽד

and then we repeat again

הֲשִׁיבֵ֨נוּ הֹ׳  אֵלֶ֙יךָ֙ וְֽנָשׁ֔וּבָה חַדֵּ֥שׁ יָמֵ֖ינוּ כְּקֶֽדֶם

Why do we repeat the next to last pasuk again?  The simple pshat is that we want to end on an uplifting note.  Rav Teichtel in his derashos Mishnas Sachir offers a different explanation.  The gemara in Brachos (7b) writes:

זמור לדוד בברחו מפני אבשלום בנו מזמור לדוד קינה לדוד מיבעי ליה אמר ר' שמעון בן אבישלום משל למה הדבר דומה לאדם שיצא עליו שטר חוב קודם שפרעו היה עצב לאחר שפרעו שמח אף כן דוד כיון שאמר לו הקב"ה הנני מקים עליך רעה מביתך היה עצב אמר שמא עבד או ממזר הוא דלא חייס עלי כיון דחזא דאבשלום הוא שמח משום הכי אמר מזמור

David said a mizmor of joy when he found out his punishment was not that he would have a child who is a mamzer or an eved, but rather than Avshalom his son would try to get rid of him.  

This is why David was happy and saying a mizmor?!  If his own flesh and blood was trying to do away with him, all the more reason he should be upset!

R' Yehonasan Eibshitz answers that there are two types of punishment.  There is one type of punishment where Hashem simply turns his back on a person or on a nation, and fate has its way with them, and there is another type of punishment where Hashem himself intervenes to afflict the person or people who need to be taught a lesson.  David haMelech was more troubled by the thought of the first punishment than the second.  If he must suffer, he thought, let it be b'yad Hashem and let there at least still be a connection.  Let it be b'yad Hashem so that what happens brings kaparah and is not simply happenstance.  

When David saw that his own son rose against him, he realized that this is something unnatural, outside the bounds of what you would expect b'derech ha'teva.  Mizmor l'David, he said, that Hashem has not tossed me to fate, but is still personally involved.  If he is involved, everything that happens is a kaparah.

We beg Hashem to put aside our wrongdoings and return us to Him because we have been in galus so long, but maybe it's just our fate to be exiles, maybe that's just how history plays itself out.  Maybe Hashem has turned his back on us and left us to the forces of teva, and our suffering has just been happenstance, not kaparah, not a result of leading to some final goal or redemption.  What right do we have to demand הֲשִׁיבֵ֨נוּ ?  Says the navi, that can't be.  כִּ֚י אִם־מָאֹ֣ס מְאַסְתָּ֔נוּ קָצַ֥פְתָּ עָלֵ֖ינוּ עַד־מְאֹֽד.  The amount we have suffered  עַד־מְאֹֽד is not normal, is beyond what any other people in history ever suffered or experienced.  It cannot be simply derech ha'teva, but rather must be yad Hashem.  Therefore, if it is yad Hashem, if everything we have gone through is for the sake of kaparah, we reiterate our request, and have every right to ask  הֲשִׁיבֵ֨נוּ הֹ׳  אֵלֶ֙יךָ֙ וְֽנָשׁ֔וּבָה חַדֵּ֥שׁ יָמֵ֖ינוּ כְּקֶֽדֶם.