In about 1539 AD, the second Sikh Guru Angad Dev Ji developed a script, Gurmukhi, from Punjabi Landa. While he used this script to write religious works in several different languages, it came to be a symbol of Punjabi — and Punjabi Sikh specifically — nationalism.
Gurmukhi is an abugida and behaves like the vast majority of the other Brahmi-derived abugidas. This is a bit surprising. First, while it is one of very few Indo-European languages to have tones, the tones are not written with diacritics, but with different glyphs for consonants on syllables with a falling tone (vs. with no change). Second, as you will recall from Sharada, Sharada dropped the vowel diacritics, so Ji had to recreate them based on one of the other Indic scripts (e.g. Devanagari).
In 1947 AD, Pakistan gained independence from India, and things got very ugly. The old Punjab region (which had historically seen lots of conflict, but been its own country from 1799 to 1849 AD) straddled the border, with more Muslims on the Pakistan side and more Sikhs on the Indian side. Both sides behaved very badly, killing lots of the minority, with the result that basically all the Pakistani Sikhs fled to India (and stayed there) and basically all the Indian Muslims fled to Pakistan (and stayed there).
Today, the Punjabi language is almost always written in Gurmukhi in India, and almost always in Shahmukhi (a variant of Arabic) in Pakistan. The writing system used is thus a marker for religious and political affiliation. A similar situation exists in the former Yugoslavia: Serbian and Croatian are essentially the same spoken language, but the mostly-Eastern Orthodox Serbs write in Cyrillic script and the mostly-Roman Catholic Croatians write in Latin script. (You might recall that the Serbs and Croats also behaved badly towards each other as the former Yugoslavia slowly fell apart.)
While writing apparently first started to make accounting easier, it is also very common for a writing system to be used (or retained) in a purely religious or ceremonial function. Of the writing systems I have already discussed, Naxi Geba, Naxi Dongba, Sharada, and the Nestorite branch of Syriac are clearly now ceremonial/religious scripts; Oracle bones Chinese was probably principally a religious script. I will cover many others as I continue this blog.