White represents not dying, both by preventing damage and by healing damage. White wins by having more health than their opponents, and outlasting them in battle.
Blue represents drawing the right card, mostly by drawing a lot of cards. Blue wins by controlling spells and hands. (When the article says "knowledge", note that the MTG deck in play is called "the library"!)
Black represents destruction. Black wins by controlling battlefields and removing blockers.
Red represents opportunities in the current moment and the random possibility of change. Red wins by playing on offensive tempo (the "upswing") and attacking vulnerable targets with instant abilities. ("Tempo" here is not quite as in music; it means playing cards turn after turn with a reliable ramping up in cost and effectiveness.)
Green represents growth and the potential for planning. Green wins by playing on defensive tempo (the "downswing") and tilting the battlefield in their favor over many turns.
Ideally, this system of categorizing by color works because there aren't any big strategies to winning that aren't color-aligned. "Milling", the strategy of deliberately destroying your opponent's library, is closely tied to blue and black, which are all about libraries and destruction. Keeping a "zoo", a battlefield full of mid-range on-tempo creatures, is closely tied to red and green, which are the two colors tied to tempo.