To have the same understanding, thought process, or amount of knowledge (about something) as someone else. We all need to be singing from the same hymn book before we try to present this idea to the boss. I think it would help if both parents attended the presentation. That way, you'll both be singing from the same hymn book when it comes time to implement what we talk about.

To have the same understanding of something as someone else; to say the same things about something as other people, especially in public. Primarily heard in UK. I think we should have a meeting with everyone who's involved in the project. That way, we'll all be singing from the same hymnbook before we begin. Make sure everyone from the campaign is singing from the same hymnbook before we release any kind of statement to the press.