Faith is the Deciding Factor - Acts 14:27

[God] opened the door of faith unto the Gentiles.

In Old Testament times, seldom did the Lord allow Gentiles to mix with Israel. The problem was that the Israelites were prone to fall to the religion of their neighbors. God's standards were higher and more difficult, and somewhat seen as a fall-back for times of crisis and war. "The Lord of Hosts" literally means the lord of armies.

There was however a clause in the law of Moses that would allow for strangers to become converted. After the Babylonian captivity, the Israelites became hardened against idol worship and never again in any real way turned back to idols.

In the days of Ezra and Nehemiah, outsiders were shunned and driven out. Even marriages to foreigners were broken up. Israel rejected all Gentiles in the interest of preserving the faith. But in the time of the Apostles, the faith was opened to all who would believe, Jew or Gentile. The only criteria for membership became faith in Christ. It was an effectual door which had been opened by God himself. This is significant since the blessings which had been promised to Abraham and his posterity were now available by adoption. The only deciding factor is faith.