I like the term "condition of repentance." (18) The Savior atoned for everyone. He knew that not all would take advantage of it, but He still did it for all. It is for each of us, but it is not free. There are conditions to repentance: a humble heart, contrite spirit, etc. Some people think that all you have to do is say you believe and you are saved, but that isn't the case. It takes work. Salvation isn't cheap but it is ours if we choose. In verse 30 is says as much. It's our choice.
It is all part of the Great Plan!
Verse 30 also clarifies that it is knowledge that sets us free. The more we know about ourselves, our nature, our potential, the more we we can do with our lives. The more we know about the Savior and His Atonement, the more we can take advantage of it in our lives. We can be free from sin, free from perishing.
It really is up to us.