כֹּה־אָמַ֨ר יְהוָ֜ה אֵלַ֗י הָלֹ֤ךְ וְעָֽמַדְתָּ֙ בְּשַׁ֣עַר בְּנֵֽי־עם [הָעָ֔ם] אֲשֶׁ֨ר יָבֹ֤אוּ בוֹ֙ מַלְכֵ֣י יְהוּדָ֔ה וַאֲשֶׁ֖ר יֵ֣צְאוּ ב֑וֹ וּבְכֹ֖ל שַׁעֲרֵ֥י יְרוּשָׁלִָֽם׃
永恆者對我如此說：你去站在百姓的城門口，就是猶大列王出入的那座門，也要站在耶路撒冷的各城門口。
Malbim
So said the Lord to me – After the Lord had decided on His decree, the attribute of mercy came back and gave them a simple solution in order that Jerusalem not be destroyed. It was that they keep Shabbat free of all desecration, as the Sages wrote ‘anyone who keeps Shabbat according to the law, even if they worshipped idols like the generation of Enoch, they will be forgiven.’ (Shabbat 118b) This is because keeping Shabbat testifies to a faith in creation ex nihilo and Divine providence, and contradicts the worship of idols. Therefore it is impossible that the sin of idolatry would cause the destruction since through the keep of Shabbat they were testifying to its opposite – that God created the world and rules over all its systems. They already said there in the gemara that if Israel would keep Shabbat twice they would be immediately redeemed (and all the more so that the merit of Shabbat would be effective in preventing the destruction of Jerusalem):
Malbim
in which the kings of Judah come – this is to give warning to the great people first:
Malbim
and out of which they go – to warn them multiple times as they go out and come in: