If you want your congregation to sing you need to show them the words of the hymns/songs that you are using.
It sounds obvious - but you may be amazed by how many church-musicians assume that "everyone knows Amazing Grace" (or whatever), and how many set up self-perpetuating situations by assuming that "people here won't sing, so we don't need to bother them."
There are some songs that are very well known. But, especially in a service that is open to everyone there may be:
- Some young people, who haven't taken any notice of the words before,
- Some older people who are struggling to remember things that used to be familiar
- Tourists and/or migrants who don't know songs that "everyone" in your country or culture knows (especially if their first language is different from yours)
- Visitors who are uncertain how you operate: they may assume that if you don't show them the words, you don't want them to sing.
- People who know several different versions of the song.
In short, if you want your people to sing you need to tell them that you want them to - and enable them by providing at least) the words that you are using today.