From a reader:
I tend to think of some of my best ideas during Mass. I keep a small notebook and a pen in my pocket. Is it permissible to jot down quick thoughts?
Sure, I think that is okay… occasionally.
That said, remember that the Actor at Holy Mass is Christ Himself. Were He suddenly to come to you more apparently, would you not give Him your full, undivided attention? I suspect that were you to be given a preview of heaven, you would focus on what you saw while it was going on, not taking your attention away to make notes.
Of course our memories, especially as we get older, are not what they used to be. Making a note helps. A good point in a sermon (or maybe even a really bad one!), a flash of insight, a memory of something from that past that you need to confess….
I think it is okay to jot something down, but Mass is not a didactic moment. Mass is not the same as Exposition of the Blessed Sacrament wherein, over the course of an hour, you might go from an intellectual exercise to meditation to contemplation and back.
An occasional note during Mass, sure. But you probably shouldn’t be sitting there regularly with pen and pad in hand.