It's easy to be church when you're at church.
But your witness is who you are when you're not at church.
Would someone you know be totally surprised to find out you go to church? Do you point people to the way of Jesus?
We can use all the right words in church, but who we are when anyone else is around is our witness. We don't get to choose if we want to be a witness.
As a Christian, you are one! The only choice you get is to determine what kind of witness you're going to be.