Although the Sundanese people highly valued poetry, he did the translation in prose hoping that it would help readers entertain new ideas.

[1] Coolsma first worked in a printer's office, but began training to be a missionary in Rotterdam in 1861,[1][2] after having studied several months under Rev.

[1][3] He finished his training on 5 May 1864; that December he left for Batavia (now Jakarta), the capital of the Dutch colony in the East Indies.

[2] Upon arrival in April 1865, Coolsma was sent by the Netherlands Missionary Union (Netherlandsche Zendingsvereeniging, NZV) to the town of Cianjur.

Eventually, according to Mikihiro Moriyama of Nanzan University, he "had a sharper insight and deeper knowledge" than contemporary missionaries and government workers.

[2] He left his school in the hands of fellow missionary D. J. van der Linden and went to Sumedang; there he worked on his translation over a period of three years.

[2] Coolsma found that Sundanese literature consisted predominantly of poetry, including the narrative wawacan, and thought that prose needed to be developed as well so that the people would embrace modernity.

[12] Ultimately, Coolsma chose to translate the Gospel of John and Acts of the Apostles using prose, believing that dangding was "too traditional to convey new ideas" and hoping to promote a "new spirit".

In 1881, he wrote a series of condemnatory reviews of Sundanese-language schoolbooks offered by the colonial government, arguing that the content had little value and the language was mostly artificial.

[2] Her death led him to reduce his workload, although he found time to publish his memoirs, Terugblik op mijn levensweg, 1840–1924 (Looking Back on my Life, 1840–1924), in 1924.

[3] Moriyama writes that Coolsma's "unrivaled" dictionary and grammar had a much greater impact than his Bible translations, serving as a basis for the standardisation of written Sundanese.