Always saw this as a somwhat depressing but objective take on the course of human history, from a vantage point far enough away to see beginning and end. Given the musical continuity it should be read in context of the next song.

The basic idea is that we started, not good nor evil, since those concepts hadnt yet been created, that we could have gone either way, but ended up being endlessly driven towards destruction.

"Light" - The lyrics recognize a sort of clean slate beginning (pure as we begin)
light is the catch-all metaphor for the beginning, be it Big Bang or God, the method is beside the point. By the end of the song, and thus by the end of humanity, light is less ambiguous, leaning more towards the light of war, nuclear explosion (though call it apocalypse if you must).

"Will" - Whenever I see this word I think of Nietzsche, where the will was a will to power, a will to take control, a will to dominate, and the idea that this simple concept could explain the entire course of human history and the driving force behind every achievement. You might view it in a more objective manner, simply describing a collective pushing through history, but this pushing itself recognizes an inherent agression through time.

The words then move rather simply through two achievements - tools/technology and fire - that have pulled us through time, their potential utility, and their ultimate use for destruction.
- Here we have a stone
1) Gather to build a home (or)
2) Throw to kill the stranger
- Here we have a fire
1) Warm our homes (or)
2) Forge a blade to destroy those of others

so you could read it simply as "yep, this stuff could be used either way". But in the context of Right in Two i think the better reading is "we keep favoring (2)".

Left only with this will to dominate, the introduction of stone and fire culminates in an angry mob tearing apart bigger and bigger castles until "light" (whether you chose God before, in which case, salvation, or Big Bang, in which case, nuclear war) removes the "will".

In a nutshell, cause that was way too long, a bleak, pointless, but honest look at human history from beginning to end. The next song zooms in somewhat arbitrarily to one point in that timeline (now) on an atomic/angelic level for more pointed commentary/lamentation on the "will" of humans.

for reflective reference:

in·ten·sion /ɪnˈtɛnʃən/
–noun
1. intensification; increase in degree.
2. intensity; high degree.
3. relative intensity; degree.
4. exertion of the mind; determination.
5. Logic. (of a term) the set of attributes belonging to all and only those things to which the given term is correctly applied; connotation; comprehension. Compare extension (def. 12)

side note... because i suddenly ifeel im in an anonymous support group, and also i owe an explanation for the length of the post - its 1am, i have 20 pages of a brief to draft by morning for law school and I just spent 45 minutes (over)dissecting a rather simple set of lyrics... mirror show me what's the difference.