First, let me point out that this question blurs Buddhism and Daoism a bit. That's understandable; Buddhism has tended to absorb and co-opt other traditions as it expanded, so a lot of our perspective on Daoism has a distinctly Buddhist flavor. But strictly speaking, concepts like 'non-attachment' are not specifically Daoist.
At any rate...
Daoism is a mystical philosophy, not an analytical philosophy. The difference:
- analytical philosophy (which makes up the bulk of modern Western philosophy) is language-centric. It tries to capture deep, fundamental concepts in language so that they can be explored and understood within explicit cognitive structures
- mystical philosophy (which covers most older philosophical schools, and persists within certain religious traditions) is apperception-centric. It holds that deep, fundamental concepts cannot be captured within the limitations of language, and can only be captured implicitly through reflection, contemplation, and experience.
The first few sections of the daodejing spell that out specifically, trying to explain that words are not going to get us to the understanding we desire, and to lead us beyond them.
If I were to summarize the philosophy (briefly and coarsely) I'd start by pointing out that the title 'daodejing' is merely descriptive. It's three words:
- Dao: the way (the way of the world); how things work; what 'is' in a dynamic, systemic sense.
- De: virtue (virtuous behavior); what we should do to work with and within the way of the world
- Jing: classical text or scripture
So we can see that daoism is a naturalist philosophy, suggesting that the world works in a certain way, and we are part of that world. The best way to live our lives comes from understanding that 'way' and conforming to it instead of fighting against it. Fighting against the way is exhausting, destructive, and ultimately futile; real virtue calls for a more finessed approach of working within the world so that the way of things naturally supports and amplifies one's efforts. The rub, of course, is that this 'way' cannot be captured in structured philosophy. That's the first line: "The way we can talk about is not the way, the word we can use is not the word". So, much of the work is an exercise in pointing and describing, trying to bring across the sense of the way without falling into the trap of denoting what cannot be denoted.
Most ancient philosophies are wrapped in religious ideation. Prior to the invention of the printing press, the only way to maintain a philosophical tradition was through oral transmission or hand transcription, which demands an organized and dedicated order of people (aka, a cult or sect). But the justification for the dao is not primarily spiritual or religious. It's philosophical: an observation that intellectual knowledge is partial and superficial, so we have to learn to see through what we know to get at understanding.
Hope that helps.