In ancient Delphi, the words "Know Yourself" were inscribed on the shrine of the oracle of Apollo. Ever since then, Western secular culture has considered self-knowledge the crown jewel of human endeavor. The Torah, in contrast, tells us "Know the G-d of your father; serve Him with your whole heart and the desire of your soul," and "Know before whom you stand." In the Torah's scheme of things, man's purpose is to know G-d, that is, to be constantly aware of His presence. This knowledge, and not awareness of himself, is what is to fill man's consciousness.
This however, creates a paradox. In order to know G-d, a person has to know himself first. For in every Jew there is a soul which may be considered a part of G-d; by coming to know the part we can come to know the whole. Man's task is therefore to unearth the G-dliness hidden within him. Although not simple, this endeavor is invaluable. Once he has attuned himself to his own Divine dimension, a person will be better positioned to see the Divinity inherent in all creation, and to sense just what his individual role is in the Creator's grand scheme.
The Torah says that G-d created the world in order to have a home in the lower realms. "Lower" does not imply physical lowliness, but lowliness on the scale of consciousness of G-d. Our physical world is on the bottom rung of a vast hierarchy of universes or orders of existence, each defined by a different grade of awareness of what and who G-d is. Our world is the lowest in that in and of itself it does not initially betray the fact that anyone created it. Nature is so perfect a disguise for the Divine power constantly creating the world that it is possible for people to be born, live their whole lives, and die without it ever occurring to them that there is a G-d. In fact, G-d is so hidden here that many intelligent people are convinced that there is no G-d.
It is this world, where Divinity is so concealed, that G-d seeks to make his home. Precisely here, where everything seems antithetical to awareness of Him, He wants everyone to be aware of His existence and establish a relationship with Him. This is why He created such a world in the first place, and this is why each individual soul, a part of G-d, is sent down here. Each individual has a unique role in achieving this goal, and the only way a person can get a sense of what his unique purpose is in this scheme is by attuning himself to the G-dliness within him.
It is in this sense and for this end, according to Judaism, that a person must know himself. By knowing the part, his Divine soul, he can get a glimpse of the whole, the essence of G-d reflected in it.