During the Messianic Kingdom there will be no unsaved person or one who engages in sinful behavior allowed in to the sanctuary in Jerusalem. During the Messianic Kingdom there will be people born to those with natural bodies. Some of them will not accept The gospel of the Messiah. They will not be allowed into the Temple for any reason. These of course are the Gentiles. God demands holiness of His people especially in the houses of worship. The Israelites were guilty of doing this and were warned not to do it when they returned after the Babylonian captivity (Ezra 4:1-3; Nehemiah 13:1-9). God demands purity of belief and behavior of His children and only the saved are to be allowed into the house of worship. The same is true of the Church although it is violated regularly.
The teaching services of the Church are meant to build up the believers in wisdom and grace. The services are not the time to evangelize the lost with their stubborn and unresponsive hearts. When the lost are allowed to participate in our services the accurate and complete teaching of God’s Word is severely impaired. The frequent practice in the modern seeker sensitive services results in critically reducing the level of teaching of God’s Word to at best a rudimentary level so as to accommodate the unbelievers. At worst it is corrupted to avoid offending those who would find it contrary to their paganized outlook on world behavior.