מִֽכָּל־מִ֭שְׁמָר נְצֹ֣ר לִבֶּ֑ךָ כִּֽי־מִ֝מֶּ֗נּוּ תּוֹצְא֥וֹת חַיִּֽים׃
Above all that thou guardest keep thy heart; For out of it are the issues of life.
Zohar
And teshuvah is called life: "because from it there are results of life" (Prov. 4:23) - those [results] are Israel's souls.