When civil war broke out in England both the Parliamentarians and the Royalists wanted the support of the Scots Covenanters who despite being ultra-Presbyterian were also very successful, having easily defeated Charles in the 'Bishop Wars' of 1639/40 - they were miserable but successful, like Andy Murray. For many in Scotland the extreme religious policies of the Covenanters went too far and there was a split between the ultra-Presbyterians who supported the English Parliamentarians and the moderates who supported the Royalist forces of Charles I. In 17th century Scotland you had a choice to make, support ultra-Presbyterianism or support the monarchy, it was 'Sophie's Choice' for Rangers supporters.

https://youtu.be/ZGsh0h7e2Gc