How are there Fourteen Links to Awakening?

The Blessed Buddha once said:
There is awareness of all internal
states, & awareness of all external states.
Both kinds of
awareness are leading to Enlightenment (sati-sambojjhanga).
There is
investigation of both all internal states, and of all external states.
Both these investigations are links to Enlightenment
(vicaya-sambojjhanga).
There is
energy of body (endurance), and energy of the mind (enthusiasm).
Both kinds of
energy are leading to Enlightenment (viriya-sambojjhanga).
There is joy associated with thinking, and there is joy without any thinking.
Both kinds of
joy are links leading to Enlightenment (pīti-sambojjhanga).
There is tranquillity of the body, and
there is tranquillity of the mind.
Both these calms are links to Enlightenment
(passaddhi-sambojjhanga).
There is
concentration during thinking and
concentration without thinking.
Both concentrations are links to Enlightenment
(samādhi-sambojjhanga).
There is
equanimity both regarding internal states and
external states.
Both these kinds are links to Enlightenment (upekkhā-sambojjhanga).
This can only a Buddha, or a true disciple of a Buddha see, and explain...

Comments:
Awareness of all internal mental states
is the most important, and highest.
Investigation
of all internal mental states is the primary, and most fruitful.
Energy of the mind is the most advantageous,
effective, and most enabling.
Joy without any thinking is the most rapturous,
ecstatic, and all-pervading.
Tranquillity of the mind is the deepest, most
calm, serene, and imperturbable.
Concentration without any thinking is the most
one-pointed and absorbed.
Equanimity regarding internal mental states
is the best guard and protection.

On the 7 Links to Awakening
(Sambojjhanga):
http://What-Buddha-Said.net/drops/III/The_Sun.htm
http://What-Buddha-Said.net/drops/III/The_Peak.htm
http://What-Buddha-Said.net/drops/III/The_Clothes.htm
http://What-Buddha-Said.net/drops/III/Rare_Emergence.htm
http://What-Buddha-Said.net/drops/III/Sequential_Seven.htm
http://What-Buddha-Said.net/drops/III/Vast_Penetration.htm
http://What-Buddha-Said.net/drops/III/The_Seven_Fruits.htm
http://What-Buddha-Said.net/drops/III/Unsurpassable_Seven.htm
http://What-Buddha-Said.net/drops/The_7_Links_to_Awakening.htm
http://What-Buddha-Said.net/drops/III/Leading_to_Enlightenment.htm
http://What-Buddha-Said.net/drops/III/The_Seven_Links_to_Awakening.htm
http://What-Buddha-Said.net/drops/III/The_Cause_of_Knowledge_and_Vision.htm
http://What-Buddha-Said.net/drops/III/The_Meaning_of_the-7_Links_to_Awakening.htm

Sources (edited extracts):
The Grouped Sayings of the Buddha. Samyutta Nikāya.
Book [V:
111] 46: Links. 52: A way of Explaining...