Why should your gates always be open?
Rashi: Their opening will be permanent.
Radak: This is Po'el Omed (the action applies only to the subject). They will be open day and night to bring to you (Yerushalayim) the wealth of nations. Targum Yonasan is like this. There will be Shalom, and they will go at night at a time of heat 1 .
Malbim: They will build a wall, but do not think that it will be needed. The enemy will not enter your gates. You will not be able to close them, for Goyim will constantly bring gifts.
I.e. in summer, when it is too hot to go during the day. When there is not Shalom, people do not go at night due to attackers. (PF)
How will their kings be conducted?
Radak: They will come in front of Melech ha'Mashi'ach like slaves in front of their master. Usually, kings ride, or officers on foot go in front of them, honorably.
Radak citing Targum Yonasan: They will be fettered. Ibn Ezra - this is like "Le'esor Malcheihem b'Zikim" (Tehilim 149:8).
Malbim: They will drag them to Yerushalayim.
