The Shlah Hakodesh (ב"י אות) on this week's parashah (on the words ואמרת וענית) writes, "Rashi writes that one tells Hashem's kindness. This is the obligation for every person... When Hashem gives him goodness, and any hatzlachah, he should praise Hashem for granting it to him, for it was given to him with Hashem's immense compassion and kindness."
Especially at the end of the year, in the month of Elul, it is time to think about all the kindness Hashem gave us throughout the year, and to praise Hashem. Even if one had an extremely challenging year, r'l, and had many tzaros, he certainly also enjoyed Hashem's chesed throughout the year. As we say in Modim, עִמ ָּ נוּ יוֹם שׁ ֶבְּכָל נִס ֶּיךָ עַל, "for Your miracles that are with us each day." Every day, Hashem does miracles and wonders for every person. Why shouldn't he praise Hashem? רַחֲמ ֶיךָ כ ָלוּ לֹא כִּי ,הַט ּוֹב, "The kind One, for Your Mercies have not ceased. ,הַמְרַחֵם חֲסָד ֶיךָ תַמּ וּ לֹא כִּי, The merciful, for Your kindness never ended." There are always many reasons to praise Hashem.
The roshei teivos of ל"אלו is וצריך להודות אפשר להודות, we can praise, and we are obligated to praise Hashem. Also, ל"אלו is roshei teivos for (Divrei HaYamim 1, 29:13) תפארתך לשם ומהללים לך אנחנו מודים, "We give thanks to You and praise Your glorious Name."
The Likutei Maharich says ל"אלו is roshei teivos for (Shemos 15:1) 'לה אשירה לאמר ויאמרו, "They spoke, saying, 'I will sing to Hashem." Because Elul is the time to praise Hashem for all the kindness we received throughout the year.
