Essentially, the historic Eastern Orthodox position is that perceived Western innovations such as the filioque are heresy and that heresy places you outside the canonical boundaries of the Orthodox Church. To be outside the church is to be cut off from the grace of the Holy Spirit given in the sacraments and therefore cut off from salvation. The basis for this claim is rooted in a particular construal of the unity of the church: Orthodox ecclesiologists taught that the church is ontologically one such that there are no schisms in the church, only schisms from her.
