“Subhuti, I do not have this thought: ‘I have spoken spiritual truths.’
If someone says I have spoken spiritual truths they are mistaken.”
The Buddha is telling us not to be attached to words and letters, which is an important teaching that the Ch’an Patriarch Bodhidharma would later give. It might be a little hard to understand but the point is that we should actualize the teaching in our lives, rather than just studying it and learning it. The teaching is something we study, but it’s also something that we do.