This loop turns a simple spark of life into an unstoppable cascade of growth. It all begins when you gain life, which triggers Light of Promise to place +1/+1 counters on Scurry Oak. That influx of counters makes Scurry Oak spawn a Squirrel token, and the very act of that token entering the battlefield calls upon Leyline of Vitality to grant you another point of life. Because that new life gain immediately loops back into Light of Promise, the entire engine feeds on itself to generate an infinite army of tokens, boundless counters, and endless life.