Well, Jesus died for ALL humans - past and present and future ones, until the end. If there would be something like "predestination" in saving, all efforts are useless. Why bother - it's already decided, right? When I read this text, I can only understand that all those who had the right spiritual disposition were saved or found to Christ in this moment. They believed - and thus were saved. But do not forget, the Bible is as well full of text's to show us to take care. Later on, Paul had to remind many congregations. You remember the text when they thought "great, Jesus died for our sins - so the more we sin, the more his sacrifice is worth.."? People come to a lot of solutions if it suits them.
Think about: Matthew 7:21-24, Matthew 25 (full chapter), Luke 21:34 ff. etc, etc. You can read as well the first three chapters of Revelation were Jesus wrote the letters to the congregations... For me, the logic of all this is: Being a Christ you only come to god through Jesus: I am the way - nobody comes to the father except through me. Then, once you are Christian, take care that you continue to follow the way - every day, all your life. 1 Peter 5-8 says: Be alert and of sober mind. Your enemy the devil prowls around like a roaring lion looking for someone to devour. There are much more texts like this.
So for me, being Christ, is a constant fight or constant attention. Sorry, EN is not my mother language. But I am sure, you understand. As for me - I am happy not to understand everything. In fact, I do not even want to. Funny is - my wife is from Africa, can hardly read (and the only thing she reads is the Bible) - but I never met a better Christian. Knowledge is not it - but the heart. And she just trusts god like a small child trusts her parents. And many small miracles happened - this is very encouraging.