De acordo com a DC Wikia (grifo meu):
All power rings need periodic recharging. The process is not instantaneous so many Green Lanterns recite an oath while the ring charges. The oath is not required to charge the ring, but is recited to reaffirm the person's commitment to the Green Lantern Corps, and to measure the time it takes the ring to charge. While many Green Lanterns create their own oath, the majority use the Corps' official oath as a sign of respect.