Ezekiel was to lie on his left side for 390 days to “carry the error of the house of Israel,” and on his right side for 40 days to “carry the error of the house of Judah,” and each day was shown to stand for a year. The two periods (of 390 years and of 40 years) thus symbolized evidently stood for the length of Jehovah’s forbearance with the two kingdoms in their idolatrous course. The Jewish understanding of this prophecy, as presented in the Soncino Books of the Bible (commentary on Ezekiel, pp. 20, 21) is: “The guilt of the Northern Kingdom extended over a period of 390 years ([according to the] Seder Olam [the earliest postexilic chronicle preserved in the Hebrew language], [and Rabbis] Rashi and Ibn Ezra). Abarbanel, quoted by Malbim, reckons the period of Samaria’s guilt from the time when the schism took place under Rehoboam . . . until the fall of Jerusalem.

From the division of the kingdom in 997 B.C.E. to the fall of Jerusalem in 607 B.C.E. was 390 years. While it is true that Samaria, the capital of the northern kingdom, had already fallen to Assyria in 740 B.C.E., in Hezekiah’s sixth year (2Ki 18:9, 10), it is probable that some of the population fled into the southern kingdom before the Assyrians’ advance. (Note also the situation in Judah following the division of the kingdom as described at 2Ch 10:16, 17.)