How to distinguish the different stages of insight in MN 24?

> In the same way, my friend, purity in terms of virtue is simply for the sake of purity in terms of mind. Purity in terms of mind is simply for the sake of purity in terms of view. Purity in terms of view is simply for the sake of purity in terms of the overcoming of perplexity. Purity in terms of the overcoming of perplexity is simply for the sake of purity in terms of knowledge & vision of what is & is not the path. Purity in terms of knowledge & vision of what is & is not the path is simply for the sake of purity in terms of knowledge & vision of the way. Purity in terms of knowledge & vision of the way is simply for the sake of purity in terms of knowledge & vision. Purity in terms of knowledge & vision is simply for the sake of total Unbinding through lack of clinging. > [MN 24](https://www.accesstoinsight.org/tipitaka/mn/mn.024.than.html) Why is the purification of by overcoming doubt i.e purification leading to Stream Entry not already the doing the next two of the purifications subsequent to it? (excluding the purification leading to Nibāna without clinging). Why are those other two purifications needed before stream entry? Surely if one has purified any one of these three it would imply the the other two?