Justification is the idea that when we do something wrong, like lying or stealing, we become separated from God. It's like a big wall comes between us and God, and we can't get back to Him on our own. But, God loves us so much that He made a way for us to be forgiven and to get rid of that big wall.
This is where Jesus comes in. He lived a perfect life and died on the cross for our sins. Because of what Jesus did, when we believe in Him and ask for forgiveness, God sees us as perfect and without sin. It's like God takes away that big wall and welcomes us back to Him with open arms. This is called justification.
So, justification is when God forgives us and declares us right with Him, even though we still make mistakes. It's only possible because of what Jesus did for us on the cross.