I have recently been looking at the concept of Remnant theology in regard to the relationship between Israel and the Church following a discussion with a Bible College lecturer. This is something that needs development I believe. The picture of God calling out a Remnant of Israelites who are faithful to Him is found throughout the Old Testament. In the New Testament a faithful remnant for instance is mentioned in Romans 11 'So too, at the present time there is a remnant chosen by grace.' (Romans 11:5).
John J. Parsons has a useful article online that discusses this in a reasonable manner Remnant Theology versus Replacement Theology, although it is necessary to do some more work in defining exactly what is meant by Replacement theology and the Church, and Remnant theology and Israel. Too often this debate is coloured by inaccurate stereotypes and woolly definitions.