When something is pure, it means that it is not mixed with something else that is irrelevant to it. For example, if you bought a sack of potatos in a store, you would expect it to contain only potatos. If after you bought a sack of potatos, you later discovered that it also had a banana, you would think it was strange. This is because a banana is an entirely different food.
If you happen to like bananas then there is no problem, but it is still not a good for all sacks of potatos to contain a banana. Some people may not like bananas and only want potatos. The point of all this is that there is nothing wrong with potatos or bananas by themselves but some things just cannot be mixed.
In the same way, some people just don’t mix. Just because you disagree with someone about something does not mean that you hate them or consider them an enemy. It can however mean that there are times when people must go their separate ways because their goals are just too different, separate, or irrelevant.
But if two or more people agree on at least one thing, then you can work together to achieve nearly anything. This is why purity is relevant. To be pure is to be a potato in a sack of potatos or to be a banana in a bunch of bananas. It is relevant to first know what you are so that you find where you belong, where you fit, where you are relevant.