Can unbelievers enter the millennial kingdom?
No, only believers can go into the kingdom, and there will be no unbelievers in the millennial reign. There will be nations again, but unbelievers are excluded. Believers will populate the kingdom age, and from them will come the great population explosion.
Les explains that Christ at His second coming will smite the nations and rule them with a rod of iron as He sets up His kingdom. He points out that there will be nations again in the kingdom, but only believers can go into it; no unbelievers will be in the millennial reign. Believers will be the early citizens or inhabitants of the kingdom age, and from them will come the great population explosion. The rider is named King of kings and Lord of lords.