By the 1860s, the annual meetings of the Zeister Zendelingsgenootschap (ZZG, Zeist Missionary Society) had evolved into much more than just a meeting where the society's formalities where rushed through. The ‘mission days’ (Zendingsdagen), as they were called, attracted around 2000 people to the small village of Zeist, most of whom would arrive by train. They would spend the day attending a service, receive updates from the foreign missionary front, enjoy each other's company, listen to ‘edifying music’ and take hikes in the surrounding forests. For these numerous visitors, it must have been an enjoyable day. For the conveners, the local Moravian church (Broedergemeente or Hernhutters), on the other hand, it was burden as they experienced difficulties in handling this number of people. One of the loyal visitors, the Harderwijk-based pastor Simon Hendrik Buytendijk, would later recall it in this way: ‘The congregation appreciated the visitors, but we should remind ourselves that good things can also come in abundance. […] To avoid the hustle during the evening sermon, I went for a walk instead. I ran into some Moravian nuns, and they expressed their lament.’ As we will later see, this experience was the incentive for Buytendijk to take the concept of mission days to the next level. The next year he organized a mission festival (Zendingsfeest), which attracted a crowd three times as large as the meetings in Zeist. It was the start of a tradition spanning decades.

The early 1860s witnessed popular demand for mission days and festivals. Apparently, there was such a thing as a missionary public: a public that showed interest in the mission and whose existence was not orchestrated top-down, as the Moravian congregation barely advertised their meetings.