The world of Beriya and Yetzira:
The difference between the worlds of Beirya and Yetzira is the level of G-dly revelation they contain. In the world of Yetzira shines the Midos, or emotional attributes of Ein Sof, as it states in the Tikkunim and Eitz Chaim that the six Sefiros dwell in Yetizra. This revelation is expressed in the creations, and angels of that world through their service of love, fear, and trepidation. This is the service of the angel’s, day and night without break. The entire camp of Gavriel stands by the left with constant fear and trepidation. The entire camp of Michael stands by the right and serves with love. However, in the world of Beriya shines the Chabad/intellect of the Ein Sof, as it states in Tikkunim that the supernal mother hovers over the three Sefiros in the world of Beriya. This intellect is the source of the Midos and is the mother and root of them. Based on the above, it is understood why the world of Beriya is the abode for Tzadikkim, as explained next.
 Tanya Chapter 39