The concluding verse of Parasha Behar, Leviticus 26:2, is one of the Torah’s many instances of summarizing proper religion in a pithy sentence.
Many people are familiar with Yeshua’s summary in Matthew 22:35-40 ("The two most important commandments..."), Micah’s summary in Micah 6:8 ("He has shown thee..."), and James’s summary in James 1:27 ("True religion is..."). Other "summary verses" in scripture include Deuteronomy 10:12 and Ecclesiastes 12:13.
Hillel had a summary very similar to Yeshua's: it included the concluding phrase "...go now and study!" Finding summaries of Torah worth pondering was actually an intellectual game among first centruy Jewish scholars.
Here in Leviticus 26:2 God offers a summary focusing on spending time with him: “Keep my Shabbats and revere my sanctuary; I am Adonai.” In other words, “Rest with me and share meals with me.” The message of Leviticus, at its core, is that simple.
There are other worthy things for congregations to do: prayer, study, charity, fellowship, outreach, etc. But none of these other activities will be help God do what he wants done and extend his Kingdom unless the congregation is resting with God and sharing meals with God. Those two activities have always been how God rejuvinates and transforms people. Once we are rejuvinated and transformed by God then we can do other activities fruitfully.