From Big Truths for Young Hearts by Bruce Ware:
Like a play that moves the story forward through its series of Act 1, Act 2, and Act 3, the salvation story of the Bible moves the plan of salvation forward through three acts.
In Act 1, Adam sins in the garden, eating the forbidden fruit, so that his sin is charged not only to him but also to all who have come from Adam (Romans 5:12-19) Just like if you used your dad’s credit card to buy something, charging the expense to him, so God charges us with the sin of Adam. In so doing, this brings to Adam and to us both the stain and bondage of sin in our inner lives and the guilts of sin before a holy God.
Act 2 involves God the Father taking all of that sin—both the sin we received from Adam and all of our own sin—and charging that sin to Christ. As we’ve thought about earlier, when Jesus died on the cross, he bore our sin and took the punishment that we deserved. Even though he was sinless and innocent of any wrongdoing, yet for our salvation, God the Father put our sin on his Son and satisfied his own just wrath against our sin through his Son’s death. As Paul states, “For our sake he [God the Father] made him [Christ] to be sin who knew no sin” 2 Corinthians 5:21a).
Act 3 is crucial to the story of salvation, and it involves God the Father now crediting us with the righteousness of his own Son when we put our faith solely in Christ. To credit means to add something positive that increases the value from what was true before. When you deposit money into a savings account, you credit the account by the amount of that deposit, making the account more valuable than it was previously. God does this with sinners who turn to Christ in faith. At the moment that they trust Christ alone for the forgiveness of all of their sins and the only hope they have of receiving eternal life, he credits them with the righteousness of his own Son. The remainder of 2 Corinthians 5:21 makes this point. The whole verse reads, “For our sake he [God the Father] made him [Christ] to be sin who knew no sin, so that in him we might become the righteousness of God.”
What do you think? At what age would a child be able to understand this explanation?