Everyone who participates in any way in a democratic political process bases that participation on one’s beliefs. Those beliefs can be religious (theological) or secular (ideological). Participation is public; beliefs are deeply personal.
One thing we all are sure about is that the beliefs of other people are things they happen to believe. However sincere, however fervent, even, they might be regarding their beliefs, and however much anyone acknowledges that other people’s beliefs are worthy of respect, in the end we all know that their beliefs are of consequence only for them, and no one else.
That attitude is absolutely correct. People have a much harder time, however, acknowledging that their beliefs are without consequence for people who do not share them. For democracy to work, all citizens must accept that, too.