Now everything will be determined not by the desire to enjoy contained within her, but she, above her own will, will want to establish the goal of her development. As the Creator wanted to do everything for her, for His creation, so she wants all her thoughts to be aimed at bestowal.
The realization of this goal is called the screen (Masach). The thought is called the reflected Light. The first action needed here is restriction (Tzimtzum). From now on, decisions are made not by my desire to enjoy, but by the screen.
The transition from a personal screen to a common one is called crossing the Machsom, the border of the upper world. The first time we act within our desire covered by the common screen is considered as crossing the Machsom.
From the 2nd part of the Daily Kabbalah Lesson 3/25/18, Talmud Eser Sefirot, Part 2