How did the forces of parliament benefit from having calvinists on their side? what unique quality did the calvinists have that proved ?

The Parliament managed a Westminster assembly in exchange of the Scottish Covenanter's military service. Their intention was to form the nation together and restore the monarchy.  Calvinists are  God-centered, this has helped them because as they form the nation, a lot of support was given to the Church.

because it makes people aware of bad activities which cause fatal disease