Justification from eternity means that, in God's eyes, we are forgiven for our sins even before we are born or commit any sins. It's like having a clean slate even before we mess it up!
Before we were born, God had a plan for our lives, and part of that plan was to send his son, Jesus, to die for our sins. Jesus took the punishment we deserved, so we don't have to. This is what we call grace, a free gift given by God to us.
When we believe in Jesus and ask for his forgiveness, God sees us as if we never sinned. This is called justification. It's like getting a ticket for breaking a rule, but instead of having to pay the fine, someone else pays it for us. So, we don't have to worry about the punishment for our sins because Jesus already paid for it.
The idea of justification from eternity can be hard to understand, but it's basically saying that God's love and forgiveness for us existed even before we did anything wrong. It's an amazing reminder that we don't have to earn God's love, but rather it's freely given.