Friends:

The initiation of deliberately directing mind for the sole purpose of exertion,
is the very first initiating sprouting arising of the ability of energy .
The growing of keen eagerness and enthusiasm under the influence of the
success of the exertion itself, expands the arising of the energy ability.
Occurrence of focused attention and consideration conditioned by
the guided control of exertion, is the arising of the energy ability.
The unification in one-pointed concentration under the condensing
influence of the exertion, adds to the arising of the energy ability.
Non-appearance of laziness is the advantage of the energy ability.
Absence of the frustration of laziness is the charm of this ability.
Entering mental absorption is the motive behind the energy ability.
Assured firmness of effort is the very power of the energy ability.
Enthusiastic pleasure & joy is the fascination of the energy ability.
The emergence of laziness is the danger for the ability of energy.
Through bold striving the ability of energy escapes from laziness.

Source: The Path of Discrimination: Patisambhidamagga IV
http://www.pariyatti.com/book.cgi?prod_id=133494

For a full Study on Energy (Viriya): The root Hero of all Success:
http://What-Buddha-Said.net/drops/III/The_Definition_of_Energy.htm
http://What-Buddha-Said.net/drops/III/The_Arising_of_Energy.htm
http://What-Buddha-Said.net/drops/III/The_Ability_of_Energy.htm
http://What-Buddha-Said.net/drops/III/The_Origin_of_Energy.htm
http://What-Buddha-Said.net/drops/Enthusiastic_is_Energy.htm
http://What-Buddha-Said.net/drops/III/Power_of_Energy.htm
http://What-Buddha-Said.net/drops/III/Ballanced_Energy.htm
http://What-Buddha-Said.net/drops/III/The_Chief_Hero.htm
http://What-Buddha-Said.net/drops/III/Energetic_Effort.htm
http://What-Buddha-Said.net/drops/III/Avoiding_Effort.htm
http://What-Buddha-Said.net/drops/III/Feeding_Energy.htm
http://What-Buddha-Said.net/drops/III/Energy_Viriya.htm
http://What-Buddha-Said.net/drops/III/Dual_Energy.htm