Kommentar zu Bereschit 30:17

וישמע אלהים אל לאה AND GOD HEARKENED UNTO LEAH —for she eagerly desired and sought means to increase the number of the tribes (Genesis Rabbah 72:5).

וישמע אלוקים אל לאה, because she had used both natural means, and then, failing to succeed, relied on prayer. She herself is on record as confirming this when she said נתן אלוקים שכרי אשר נתתי שפחתי לאישי, “G’d has given me my reward for having offered my handmaid to my husband. Giving Zilpah to Yaakov was considered by her as a way of relying on natural means of having more children, seeing she had come to the conclusion that she could not have any more from her own womb.

וישמע אלוקים, G'd heard, etc. This means that Leah prayed to G'd first.

וישמע, when the Torah speaks of “the fifth son,” “the sixth son,” this is to remind us that this woman was deemed worthy to bear half of the 12 founding fathers of the Jewish nation.

She desired and sought to increase the number of tribes. [Rashi knows this] because normally the phrase וישמע אלהים pertains only if one prayed. But here it is not stated that she prayed for sons. Thus Rashi explains, “Because she desired...” I.e., since she so wished to increase the tribes, it was considered as if she prayed for this — and Hashem granted her wish.

It may also mean that G'd had understood the reasons for Leah's behaviour. She was motivated by her love for G'd and her desire to fulfil His commandments. If, in the process, she had committed an error of etiquette, G'd on His part did the same by allocating to her more than the four sons originally intended. The other two sons were in recognition of Leah's pure motives.