A mechanicistic view is only necessary if God is mostly "hands off". Alternatively, God could be regularly be tweaking things to make sure his plan happens.
It's also worth noting that both Thomas Hobbes and JJ Rousseau came from Calvinist circles. So I don't think it is an exaggeration to say that the Hobbes/Rousseau (and those closely influenced by them, such as those of Locke) are effectively Calvinism as applied to society and clothed in secular rhetoric.