When a person praises Hashem for His kindness, he will receive more. It can be compared to when a mother gives a meal to her son. If he praises his mother and tells her how good it tastes, the mother desires to give him another portion. Similarly, when we praise Hashem, Hashem wants to give us more.
This is written in the Siforno in last week's parashah (27:27). When Yaakov brought food to Yitzchak, the pasuk states, רְאֵה וַיֹּאמֶר וַיְבָרֲכ ֵהוּ ...'ה לך ויתן ,'ה בֵּר ֲכוֹ ֶׁראֲש שָׂדֶה כְּר ֵיחַ בְּנִי רֵיחַ, "He blessed him, and he said, 'Behold, the fragrance of my son is like the fragrance of a field, which Hashem has blessed! And may Hashem give you...'"
The Siforno writes, "You, my son, see and think about this smell. In addition to the fact that food gives life, it also has a pleasurable smell. This is an example of Hashem's kindness. When you think about Hashem's kindness, האלקים לך ויתן, Hashem will give you more blessings." This is as we are explaining; the more a person recognizes Hashem's kindness, the more he will receive.
It states (29:35) אוֹדֶה הַפַּעַם וַת ֹּאמֶר בֵּן וַתֵּלֶד עוֹד וַתַּהַר יְהוּדָה שְׁמוֹ ק ָרְאָה כֵּן עַל 'ה אֶת, "She conceived again and bore a son, and she said, 'This time, I will thank Hashem!' Therefore, she named him Yehudah." Maharam Shik writes, "When a person has genuine hakaras hatov, it isn't enough to praise Hashem once. The praise of Hashem should always be engraved in his heart. This is the reason the Avos would name places in commemoration of a miracle or a kindness that occurred there. They did this always to remember the chesed that happened to them. It was also for the future generations, until the final generation, that they should praise Hashem for His chesed, as there is a brachah: לאבותנו ניסים שעשה ברוך, 'Bless Hashem Who performed miracles for our forefathers...' The tzadekes Leah would also do this. She made signs to remember... and never to forget to do her obligation to praise Hashem for His kindness. When her fourth son was born, which was more than her portion, she wanted to remember to praise Hashem for His kindness. She said to herself, 'After all this kindness, is it enough to praise Hashem once? I should always be praising Hashem. His praise shouldn't leave my lips. Therefore, she called him יהודה, to remember her love for Hashem. Whenever she would say her son's name, she would remember Hashem's kindness. Therefore, Leah said, 'ה אֶת אוֹדֶה הַפַּעַם which should be read as a question, 'Should I praise Hashem only once?' It isn't proper for me to do so. I should praise Hashem all the time. ק ָרְאָה כֵּן עַל יְהוּדָה שְׁמוֹ, therefore, she called his name Yehudah, which means to praise Hashem constantly.
Leah called her third son Levi. As it states (29:34) כִּי אֵלַי אִישִׁי יִלָּוֶה הַפַּעַם עַת ָּה וַת ֹּאמֶר בֵּן וַתֵּלֶד עוֹד וַתַּהַר לֵוִי שְׁמוֹ קָרָא כֵּן עַל בָנִים ָׁהש ְׁלֹש לוֹ יָל ַדְתִּי, "She conceived again and bore a son, and she said, 'Now this time my husband will accompany me, for I have borne him three sons; therefore, He named him לֵוִי" (because לוי means ילוה, accompanied).
Rashi (29:34) writes, "The Imahos were nevios (prophets), and they knew that Yaakov would bear twelve tribes. He married four wives. Leah said [when Levi was born], Now he won't be able to complain about me because I took all my portion in the children." Four wives were to bear twelve children, and when Levi was born, Leah said that she had done her portion.
When Yehudah, her fourth son, was born, Leah said (29:35) 'ה אֶת אוֹדֶה הַפַּעַם וַת ֹּאמֶר, "This time I will praise Hashem." Rashi (29:35) writes, יותר שנטלתי .אודה הפעם להודות לי יש מעתה ,מחלקי, "Now I will praise... because I took more than my portion. Now I must praise Hashem."
The meforshim explain that she wasn't only praising Hashem for her fourth child. She realized now that she should praise Hashem for her first three children as well. When she saw Hashem's chesed that He gave her more than her portion, she understood that the first children she bore were also Hashem's kindness and not nature, which is so easily taken for granted.
Tiferes Shlomo (Moadim, Tefillah) explains the pasuk (Tehillim 107:1) טוֹב כִּי 'לַה הֹדוּ, when one praises Hashem for His kindness, לְעוֹלָם כִּי חַס ְדּוֹ, the kindness will continue forever. Also, it states (Ibid. 107:8) חַס ְדּוֹ 'לַה יוֹדוּ, when one praises Hashem for the salvation, even before it comes, אָדָם לִבְנֵי וְנִפ ְלְאוֹתָיו, he will merit that the salvation will come, and then he will publicize the miracle to people.
It states in parashas Toldos (25:21) יִצְחָק וַיֶּעְת ַּר אִשְׁתּוֹ רִבְקָה וַתַּהַר 'ה לוֹ וַיֵּעָתֶר הִוא עֲקָרָה כִּי אִשְׁתּוֹ לְנֹכַח 'לַה, "Yitzchak prayed to Hashem opposite his wife because she was barren, and Hashem accepted his prayer, and Rivkah his wife conceived.
Rashi writes that Yitzchak davened in one corner, Rivkah davened in another corner, and they prayed for children. They were barren for so long, we might assume that their tefillos were sent up to Hashem through bitter crying. However, it is written in sefarim that לְנֹכַח is roshei teivos for נשמת חי כל, because Yitzchak and Rivkah established this tefillah. Even when they prayed for children, their request was dispersed within many praises to Hashem for His kindness. Hashem answered their tefillos and praises and gave them offspring.
At the end of Nishmas we say, ישרים בפי תתרומם, etc. Rokeiach writes, "It is said that Yitzchak and Rivkah composed this tefillah when Yitzchak davened opposite his wife for children. This was the kabbalah of the Anshei Kneses HaGedolah, and the tefillah was established to be said here... In honor of Yitzchak and Rivkah, the custom is that just the chazan says it, that in their merit, Hashem should do kindness with us."
