Yaakov recieves a new name - Yisrael. The Sfas Emes explains the meaning of each name. Yaakov refers to navigating the crookidness of this world. Yisrael refers to the higher and deeper aspect of the Jew, rooted beneath the kisei hakavod, where everything is straight and clear. Yaakov went out of his natural level, down to the lowest point, in order to fight the angel of Esav at every level. By doing this, he created the ability for all his descendants to be able to navigate this world and find a path back to the heavenly throne from any given point. During the six work days, we work mainly on the aspect of Yaakov. On Shabbos, we rise to the lofty level of Yisrael. At that level, we feel our neshama in a much stronger way. Our Sages refer to this clarity as the "Neshama Yeseira."