Halakhah sa Isaias 40:1: Mishneh Torah, Prayer and the Priestly Blessing, Abudarham & Shulchan Arukh, Orach Chayim

The people have the custom of reading on the three Sabbaths before the Ninth of Ab, as lessons from the Prophets, passages of an admonitory character. On the first of these Sabbaths, the lesson from the Prophets is the section beginning, "The words of Jeremiah" (Jeremiah 1:1-2:3). On the second Sabbath, that beginning, "The vision of Isaiah" (Isaiah 1:1-20). On the third Sabbath, that beginning, "How is the faithful city become a harlot" (ibid. 1:21-2:4).^*Ashkenazi custom is to read respectively on these Sabbaths before the Ninth of Ab, Jeremiah 1:1-2:3, 2:4-28 and Isaiah 1:1-27. On the Sabbath after the Ninth of Ab, the lesson from the Prophets is the section beginning, "Comfort ye, comfort ye, my people" (Isaiah 40:1-26). It is the general custom in our city to read comforting messages from Isaiah as the lessons from the Prophets on the Sabbaths after the Ninth of Ab till the New Year. On the Sabbath between the New Year and the Day of Atonement, the lesson from the Prophets is the section beginning "Return O Israel" (Hosea 14:2-10).

VaEtḥanan (the seven of comfort, NV' ARQ Sh): Naḥamu, Isaiah 40:1–26.

And the Midrash punningly says that they established to say at the beginning of the prophetic readings of consolation "Comfort, comfort my people" (Isaiah 40:1) — that is to say, the Holy Blessed One said to the prophets, "Comfort, comfort my people!" Upon this the congregation of Israel responds, "But Zion says, 'the LORD has abandoned me!'" (Isaiah 49:14) that is to say, "I cannot be reconciled to the comfort of the prophets." And it says "Rise, rise, dress in strength, arm of the LORD; rise as days of old!" (Isaiah 51:9). And in places where it they conclude in place of this prophetic reading "Unhappy, storm-tossed" (Isaiah 54:11), it is as if to say the prophets respond and say before the Holy Blessed One, "Lo, the congregation of Israel is not reconciled to our comforting!" Upon this the Holy Blessed One responds and says, "I, I myself will comfort you" (Isaiah 51:12), and what's more, "Rejoice, barren one without children" (Isaiah 54:1), and what's more, "Rise, shine, for your light has come!" (Isaiah 60:1). To this, the congregation of Israel responds, "I will rejoice, rejoicing in the LORD" (Isaiah 61:10), that is to say, now I have something to rejoice and celebrate! "My soul will cheer in my God, who clad me in clothing of salvation" etc.