[1] August Theis led a group of German missionaries to spread Christianity to the Simalungun area after he received a telegram from the local Rheinische Missionsgesellschaft (RMG - Deutschlands-based sending institution) leader.
2 September has been celebrated each year by GKPS all over the world as an olob-olob (Simalungunese for joyous) day to thank God that the Bible has entered Simalungun.
The sending mission was effectively started in 1904 with August Theis at Pematang Raya and Guillaume at Purba Saribu (western part of Simalungun).
On this occasion, some Guru (teachers) and Sintua (deacons) agreed to found a committee which planned to translate church-related text books into the Simalungun language.
In order to serve the Simalungunese better, GKPS founded its educational center at Pematang Raya and a dormitory for boys and girls.