God has called you to be a citizen, but he hasn’t necessarily called you to be a voter. God gives all of us various vocations—various stations in our life through which we are to serve our neighbor. And all of these vocations fall into one of two categories: inherent vocations and voluntary ones.
Citizen is an inherent vocation. You received it by virtue of being born under an earthly government. Just as a son can’t opt out of his God-given duty to honor his father and mother, you can’t opt out of your duties as a citizen—namely the duties of paying the taxes and obeying the laws that enable the government to serve your neighbor.
Voter, however, is a voluntary vocation—or, at least, it’s a voluntary sub-vocation of citizen in our representative republic. Like that of husband or wife, voter is not a vocation that God makes mandatory. It’s one he makes available, and the only time you’re required to fulfill that vocation is after you chose to take it on.