大般涅槃經義記 4.256

4.256

第二益中，是獲大護法說明益，真常三歸能護眾生，故名為護。覆護中勝，是以言「大」。由正知故，為彼覆護，是以言「護」。「如呪生果」喻說顯益，三寶如呪，身如枯樹，歸真三寶能成行德，如呪枯樹能生果實。

In the second, regarding benefits: this is an explanation of the benefit of obtaining great protection. The truly eternal three refuges can protect sentient beings, hence they are called "protection". Among forms of shielding and protection, it is supreme, which is why it says "great". Because of correct knowledge, one is shielded and protected by them, which is why it says "protection". "Like an incantation producing fruit" is an explanation through metaphor to reveal the benefit: the Three Jewels are like the incantation, and the body is like a withered tree; taking refuge in the true Three Jewels can accomplish the virtues of practice, just as chanting an incantation over a withered tree can make it yield fruit.