Musar zu Bereschit 30:15

After having seen the ladder in his dream, Jacob understood a number of things; among them he understood the meaning of the four exiles he had seen in his vision, and he understood the eventual redemption. This is why he said: "Indeed G–d is in this place, אכן יש ה' במקום הזה, but I did not know it." He expressed his new found-understanding that the third Temple would lead to the realization of הזה and יש. He realized that this והתהלכתי בתוככם would be fulfilled במקום הזה. These two realizations all resulted from the וישכב, when he lay down to sleep. Concerning this experience we find an allusion in Jeremiah 31,16: יש שכר לפעולתך, "there is a reward for your labor." An example of the reward for וישכב, is the incident of Leah having traded the mandrakes her son Reuben had found in order to have an extra night with Jacob. Rachel had agreed with the words : לכן ישכב עמך, "therefore he may lie with you." When Leah became pregnant as a result of that night, and Issachar who founded the tribe that excelled in Torah study was born, she stated: נתן אלוקים שכרי, "G–d has given my reward." It was Issachar who would excel in bringing about the period described as ומלאה הארץ דעה, that the earth would become full of knowledge (of G–d).