Of Indonesia's 1,311 ethnic groups, one of the largest-with a population of 8.5 million (3.6% of the national population)-are the Batak. Several sub-groups are recognized, including the Batak Angkola, Batak Karo, Batak Mandailing, Pakpak Dairi, Batak Simalungun, Batak Tapanuli, Batak Toba, and Batak Dairi. Most Bataks practice Christianity, and they have established numerous churches with their own unique characteristics, including the Batak Christian Community Church (GPKB), Karo Batak Protestant Church (GBKP), and Christian Protestant Angkola Church (GKPA). Still others have congregated in churches that do not forefront their Batak identity, showing a diversity that underscores the diversity of religious life in Indonesia. This study examines Indonesian Batak Christians' decision to congregate in a church using social identity theory as well as intra-cultural communication theory. It underscores that ethnic groups' culture and customs are closely related to these groups' specific identity and holds that personal identity cannot be separated from group identity. This study uses a qualitative approach, with in-depth interviews being conducted with members of HKBP Church, one of the oldest and largest churches in Indonesia and Southeast Asia (Saragih, 2013). It shows that parents who had Christian and Batak identities motivated their children's decision to join the HKBP Church, and that their Batak identity is more substantially used to advance their group than their other identities.