In 1603, the Heren XVII (board of directors of the VOC) "ordered that enquiries be made for two suitable and qualified persons to carry God's word, and from the Scriptures to exhort folk against all superstition and the seduction of Moors and Atheists".

This stipulated, among other things, that the company would pay his theology studies at the University of Leiden and that he would then leave for the Dutch East Indies in the service of the VOC.

During his final exam in Middelburg, concerns were raised against Slatius because he was a proponent of Arminianism based on the ideas of Jacobus Arminius.

Deeply alienated by this, Slatius and others, including Oldenbarnevelt's sons Willem and Reinier, plotted an attempt on Prince Maurice's life.

He disguised himself in peasant clothes and travelled via Amsterdam, Leeuwarden and Groningen to Drenthe, intending to escape to Germany.

The artist Claes Jansz Visscher (1587–1652), a strict Calvinist, engraved a print showing the imprisoned pastor Slatius, dressed in peasant clothes and chained hand and foot.