Exactly that. And, if one of those top 4000 do not wish to join, they are bumped down the ladder of how "good" they are, as an unwilling soldier is next to useless, and in some cases even dangerous. Rince and repeat until you have 4000 willing soldiers, which isn't at all difficult to scrounge up in a country like Sweden with such a large percentage of youth.
Anecdotal evidence, from me; had several mates back in 2006 who wanted nothing but to join the army with the rest of us in 2007, but they didn't make the cut and were denied even though medically there was nothing wrong with them. If there's a surplus of willing, able soldiers, why force others?
Sorry, I'm starting to repeat myself.