I write unto you, little children, because your sins are forgiven you for his name's sake (I John 2:12).
This verse is talking about Jesus and telling us that our sins—past, present, and future—are forgiven for Jesus' name's sake. This is great news because when our sins are forgiven, we have eternal life in heaven with God. But how can this be? Let's say that a man walked into a car dealership, bought every car on the lot, and told the dealer to keep the cars there until he came to possess them. That man could take some or all of the cars home today, or anyone he designates could walk into that dealership at any time in the future and drive any of those cars away. The cars have been paid for and can thus be taken freely at any time.
It is somewhat like that with Jesus and His having paid for all of our sins with His suffering on the cross at Calvary. Jesus grants the forgiveness sins that He has already paid for to whomsoever He chooses. And God tells us whom Jesus will choose. God tells us in the Bible that Jesus will give that forgiveness to everyone who believes in Jesus and the sacrifice He made for our sins (Acts 16:31). May we always praise our great Savior and, out of gratitude for His great gift, seek to do the things that He tells us in the Bible we should do.