As the first in a number of examples or reasons.
As a single given example, often the most obvious or important one and almost certainly enough to sway the argument, of several reasons for something.
As one person among other people who may not hold the same opinion.
I know you may not agree but I, for one, think we should get rid of this unfair piece of legislation.
First in time.
In front, prominently forward.
Most importantly.
Positioned in front of (all) others in space, most forward.
Coming before (all) others in time.
Closest to the bow.
Of the highest rank or position; of the greatest importance; of the highest priority.