meditation on selflessness self-mastery continual awareness

The greatest achievement is selflessness.
The greatest worth is self-mastery.
The greatest quality is seeking to serve others.
The greatest precept is continual awareness.
The greatest medicine is the emptiness of everything.
The greatest action is not conforming with the worlds ways.
The greatest magic is transmuting the passions.
The greatest generosity is non-attachment.
The greatest goodness is a peaceful mind.
The greatest patience is humility.
The greatest effort is not concerned with results.
The greatest meditation is a mind that lets go.
The greatest wisdom is seeing through appearances.
By Atisha

some of the concepts you need to understand or think about etc to understand buddhist concepts better.

but also applies to other religions as well, as they all have greater depth, just not always instantly apparent, have to think on deeper, more focused levels.