Remember when your parents and/or teacher insisted that the third grade is very important because if you didn't pay attention in third grade, you wouldn't do well in fourth grade and so on and so forth until it got to: 'And if you don't do well in high school, you won't get into a good college. And if you don't get into a good college, you won't do well in life'?
The same concept is in play during the NFL offseason. OTAs lead to minicamp, which sets the stage for training camp, which determines where everyone plays during the preseason, which in turn sets the table for the regular-season opener.