If they would put away their idolatry consistently and would swear by Him, rather than by the idols, then Israel would become responsible for the nations blessing themselves (cf. Genesis 12:3; Genesis 18:18; Genesis 22:18; Genesis 26:4; Isaiah 2:3; Isaiah 65:16; Isaiah 65:18). That Isaiah , the Gentile nations would come to the Lord and so experience His blessing and would glorify Him. [source][source][source]
". . . they will discern in the example of Israel that the source of true blessing lies in Yahweh and that he dispenses his blessings to those who are obedient to his covenant..." [1][source]
"Swearing by the Lord" means acknowledging Him as master in contrast to Lord Baal (lit. master) and other lords. [source][source][source]