A Christian once defined his religion to me thus;
Salvation;
By Grace alone,
Through Faith alone,
In Christ alone.
Brevity invites problems, as we well know. But were I to aim for that level of terseness it would go something like this:
Happiness;
In just one natural life--
In one uncreated, everlasting
And endless cosmos--
Through pleasure, friendship,
And fearless inquiry
Into the nature of things.