Concerning the Obligation of Each Person to Study the Wisdom of Kabbalah
The whole part of the revealed Torah [known to the masses] is but a preparation to become worthy and merit attaining the concealed part. It is the concealed part that is the very wholeness [methodology] and the purpose for which man is created.
Hence, clearly, if a part of the concealed part is missing, although one may keep the Torah and observe its commandments in the revealed part, he will still have to reincarnate to this world and receive what he should receive, namely the concealed part, by way of 613 deposits. Only in that is the soul completed, the way the Creator had predetermined for it.
– Baal HaSulam, “Introduction to the Book, From the Mouth of a Sage”