When Israel’s light shines, kings will flock to Zion to “serve” (sharat) Israel. The word typically describes priestly ministry. In the Pentateuch “stand to serve” is a thumbnail description of priestly ministry (Numbers 16:9; Deuteronomy 10:8; 17:12; 18:5, 7), and sharat also describes priestly ministry in the post-exilic Chronicles (1 Chronicles 15:2; 16:4, 37; etc.).In other contexts, it refers to a personal attendant - Joshua “serves” Moses (Joshua 1:1).
Isaiah uses the verb to describe the incorporation of Gentiles into the Lord’s service. They are “joined” (lavah) to Yahweh to serve Him (sharat). Lavah is the etymological root of the name Levi (cf. Genesis 31), and so we can speak of Isaiah’s vision for the “Levitification” of the Gentiles.
In Isaiah 60, not only Gentiles but Gentile kings become priestly servants, not to Yahweh directly but to Yahweh’s city and people (v. 10). This is an expression of Yahweh’s compassion for His people: Once He used Gentile kings to discipline Israel; now He uses them to serve and build His people. Israel will know that Yahweh has turned from wrath to compassion when Gentile kings start building their walls (v. 10 again).
Kings from the nations turn to priests of Yahweh, without ceasing to be kings. This is the political hope of Israel:Kings turned into household servants in Yahweh’s courts.