There are a few secular countries in the world. In those countries, for example, it's forbidden to teach religion in a state school.
Where I come from there was no RE, no worship at school, no nativity play, no hymns sung at school. No visiting a church. And as someone who practiced a different religion I never felt uncomfortable.
I was really shocked when I sent my first child to nursery / school to find he was in a nativity, going to church (occasionally), listening to sermons from a priest / vicar (once a month) and praying daily. At a state non faith school. And all without telling me or asking for my permission.
I was truly shocked.
It is this which makes us a Christian country not a secular one.
Nothing to do with our weekends or Christmas or Easter. Secular countries do them too. But they never make anyone, like school children, pray or go to church or listen to a sermon from a religious leader.
Honestly, I was so shocked / upset to find out my 4 year old was in a nativity play. Never ever occurred to me that a state school would put one on. (Now I know that it's every single school that does that. But you don't know that before your child goes to school. )