The Tanya seeks to demonstrate to the "average" man or woman that knowledge of God is there for the taking, that spiritual growth to ever higher levels is real and immanent, if one is willing to engage in the struggle.
"The thing is very nigh unto thee, in your mouth and in your heart to do it" (Deuteronomy 30:14).
The Tanya, then, does not create a system.
Instead, it clothes the essence of the system in structures that bring them to a level that is both higher and more revealed than anything that a story, a Hasidic maxim, a feeling, or a personal relationship could ever do.
This, then, is how we should interpret the reaction of Rabbi Zusha of Anipoli, upon receiving this book:
"I wonder how he managed to put such a great and awesome God into such a small book!"
–Rabbi Adin Steinsaltz
From the Preface to Learning from the Tanya bi Rabbi Adin Steinsaltz