ברכות א:א פירוש: עיקר תוספות יום טוב, ברטנורא והסבר באנגלית

From When. The Tana is referring to a Possuk as it says in the Possuk, "When you lie down and when you get up." From there we learn that it is an obligation on each man to read Shema in the evening and in the morning. And the Mishna now asks when is the time? and from the Possuk that says when you lie down at the beginning, we start with the evening Shema.

מאימתי קורין את שמעו בערבית? משעה שהכהנים נכנסים לאכול בתרומתן – Kohanim (Priests) who became defiled and immersed [in the Mikveh/Ritual Bath] are not able to eat of the Terumah/heave offering (2% of a yield that a person initially tithes for a Kohen), until after sunset, which is, (at the time) when the stars appear. And the fact the Mishnah does not teach, “from the time when the stars appear” is an incidental matter, which comes to tell us, that if Kohanim were defiled with an uncleanness whose purification is dependent upon [the offering of] a sacrifice, such as one afflicted with gonorrhea or leprosy – their [form of] atonement does not prevent them from eating the heave offering, as it written (Leviticus 22:7): “As soon as the sun sets, he shall be pure; and afterward he may eat of the sacred donations [for they are his food].” The setting of the sun prevents him from his eating the heave offering, but his atonement [sacrifice] does not prevent him from eating his heave offering.

Introduction Tractate Berakhot begins by discussing what time the Shema (only two paragraphs were recited at night, Deuteronomy 6:4-9 and 11:13-21) is recited in the evening. It probably begins by discussing the evening Shema because in rabbinic thought the day begins at night. This is also the order reflected in Deuteronomy 6:7 and 11:19, “Recite them…when you lie down and when you get up.” In our mishnah the sages debate what the halakhic meaning of the words “when you lie down” really are.