'Bestir' often implies someone is currently inactive and needs to begin doing something productive or important. The coach told the players to bestir themselves for the upcoming match.
Pro Tip 2/3
Self-Motivation
When 'bestir' is used reflexively, as in 'bestir oneself,' it suggests self-motivation, taking personal initiative. I had to bestir myself to finish my thesis on time.
Pro Tip 3/3
Effort Required
'Bestir' implies that there is effort involved in the action one is being encouraged to undertake. We must bestir ourselves to solve this complex problem.