In this sutta, the Buddha teaches us how to avoid conflict.
This refers to conflict when discussing the pursuit of pleasure, the pursuit of tiring meditation practices and when using idiomatic language when teaching.
The Buddha encourages us to not indulge in the pleasures of the five senses because they don't lead us out of samsara. And he encourages us to not indulge in practices that weary and tire us because they are painful and pointless. Instead he teaches us to follow the middle way which leads to direct knowledge, peace and Awakening. Direct knowledge means understanding something for oneself....not just intellectually understanding it from another. This middle way is the Noble Eightfold Path.
Given this teaching, the Buddha exhorts us to not praise or flatter someone who follows this teaching. And he exhorts us to not criticize someone who doesn't follow this teaching. Instead he teaches us to not mention the person, to just teach the Dhamma. So we would say, “Not indulging in sensory pleasures leads to Awakening. Indulging in sensory pleasures or practicing in a way that causes weariness does not lead one out of samsara. Instead, sensory pleasures and wearying practices lead to pain, harm, stress, and fever (feeling agitated).
The Buddha goes on to say that we should not speak behind people's backs and we should not speak sharply to others. If we need to do this, only do so if what we are saying is true, is going to be beneficial, is done at the right time (not when the other is busy or tired etc) and it's done privately, not in public.
Now for the good news! The Buddha exhorts us to pursue the pleasure of the mind, inner bliss. The middle way is not a miserable path. It's a path that offers a pleasure that is greater than any sensory pleasure we can experience. This is the bliss that arises in the jhana states. In our meditation practice, we seclude ourself from the sensory pleasures and from unskilful qualities and use our breath (or another meditation object) to still our body and mind. When our body disappears from our awareness, then pleasure arises in the mind. This is when we can let go of the breath as our meditation object and switch to using the pleasure as our meditation object. This pleasure leads to the jhana states......blissful states. They are the pleasure of renunciation, seclusion, peace and Awakening.
Finally, in this sutta, the Buddha comments on the use of language when teaching the Dhamma. He exhorts us to use the local language and idioms so people can understand the teachings. He encourages us to not be attached to our own idiomatic expressions or to use them with people unfamiliar with them.
A comment from Ajahn Brahm on a couple of the word translations of this sutta:
The translation says, “Don't indulge in self-mortification”. The actual translation is, “Don't indulge in practices that weary or tire you”. This is much more inclusive. It includes extreme practices like self-mortification but also includes situations like struggling to continue meditating when in pain or very tired.
Re sensory pleasures, the translation “filthy”, actually means pissy. (Amazing that this idiomatic expression has endured to the present time!) And the translation”vulgar” means “of the common people”.
Finally, when the translation says, “Insisting on local terminology”, the Buddha is not referring to the local terminology of the people one is teaching. He is asking us to not insist on our own local terminology when teaching people in a different location. It's a bit confusing the way it is worded in the translation.