-아/어야 and its more formal form -아/어야만 state an indispensable condition for some desired outcome.
-면 (as in 하면) states an ordinary condition, as in "if you do A, B happens".
-야(만) is stronger, as in "only if you do A, B may happen", or "unless you do A, B won't happen".
It also has another use usually in the form of -아/어 봐야 (소용없다 / 별수 없다), which means "Even if you do something, it's no use".
Here are some related phrases based on a simplified version of your sentence.
1. 사랑을 알아서 세상을 안다 = Because I/you know love, I/you know the world.
2. 사랑을 알면 세상을 안다 = If you know love, you know the world.
3. 사랑을 알아야(만) 세상을 안다 = Only if you know love, you may know the world.
4. 사랑을 알지 못하면 세상을 알 수 없다 = 사랑을 모르면 세상을 모른다 = If you don't know love, you don't know the world.
For example, if someone is very quiet and won't say anything, you might say to him:
- 말을 해야 (뭘 원하는지) 알지 = Only if you tell me, I'd know what you want.
== 말을 안 하니까 (난 네가 뭘 원하는지) 몰라 = I don't know what you want because you don't tell me.
- 물에 들어가야(만) 고기를 잡을 수 있다 = You can only catch fish by getting into the water.
And here's a sentence using the other use of -아/어야.
- 말을 해 봐야 소용없어 = 말을 해도 소용없어 = It's no use to talk to them = Talking to them won't change anything.