It is an orientation towards the "future" long term happiness.
"Then there is the case where a monk, having gone for alms in a village or town, does get as much coarse or refined food as he needs to fill himself up. The thought occurs to him: 'I, having gone for alms in a village or town, have gotten as much coarse or refined food as I need to fill myself up. This body of mine is light & suitable for work. Why don't I make an effort for the attaining of the as-yet-unattained, the reaching of the as-yet-unreached, the realization of the as-yet-unrealized?'[1] So he makes an effort for the attaining of the as-yet-unattained, the reaching of the as-yet-unreached, the realization of the as-yet-unrealized. This is the sixth grounds for the arousal of energy.