首楞嚴義疏注經 5.319

5.319

如來知我有辯才智，遂教我以口輪說法，此則示令不以生滅心行說實相法，故能隨說法淨即智慧淨，隨智慧淨即其心淨也。師子吼者，無畏說也。

The Tathāgata knew that I had the wisdom of eloquence, and so instructed me to expound the Dharma with the wheel of the mouth; this showed that one should not preach the Dharma of the real mark with a mind of arising and ceasing, so that as the preaching of the Dharma is purified, wisdom is purified, and as wisdom is purified, the mind is purified. The 'lion's roar' is fearless preaching.