Ideas to Contemplate When Meditation is Difficult

I wrote previously that somehow, my meditation practice suddenly became more difficult, without any cause. So, I wondered what measures could be taken. Since my objective -- for now -- is meditation *once* per day, any means by which I'd sit and meditate for an allotted time would be useful. I wondered: what reasons/motives can one contemplate mentally to get that push and sit more easily? For example: - "Once I will sit down, the difficulty will diminish." - "This is part of a path leading eventually to Buddhahood." - "Meditating will help not only myself, but others." I guess I'm looking for canonical or traditionally given reasons to invoke to motivate oneself to meditate or practice in any form. Thank you.