God made His covenant with Old Testament Israel, a type of the church (Galatians 6:16). God's focus and concern were overwhelmingly on them, and He dealt with other nations only as they came in contact with Israel. Though God makes provision in His law to accept non-Israelites who wanted to join Israel and worship the true God, He nowhere commands the Israelites to go out and make disciples of other nations. Rather, His approach is to attract outsiders by the example of obedient Israel being blessed by Him.
John W. Ritenbaugh
Who Is Doing the Work of God?
The Hebrew language lacks an exact equivalent to the Greek noun proselyte, which means a newcomer (Strong's #4339). However, in the Old Testament, God's law does allow the ger (Strong's #1616), usually rendered "stranger," to become a full-fledged citizen of Israel. To do this, he needed to become circumcised. Exodus 12:48 addresses this changing of belief system in reference to the Passover.
The stranger "wants to keep the Passover." There is no hint of God expecting Israel to seek converts among the heathen by actively preaching to—or, at—them. Here, there is no coercion, subtle or otherwise; the Gentile convert voluntarily gives himself to come under the Old Covenant. Deuteronomy 4:5-7 states the dynamics of this conversion.
Proselytism Yesterday, Today, and Tomorrow (Part One)
Other Forerunner Commentary entries containing Exodus 12:48: