Heidelberg Catechism, Lord’s Day 5
Well, says Heidelberg: our debt needs to be paid, either by ourselves or by someone else. But we can't pay it (running up further bills every day). And neither can any other creature (which would be unfair anyway). So the only possible mediator and deliverer we can hope for is one who is both fully human and fully divine, fully created and fully righteous.
At this point, we have to wait for the next Lord's Day to find out what happens next. If you don't know how the story ends, that's quite a cliffhanger.]
Q12. According to God’s righteous judgment
we deserve punishment
both now and in eternity:
how then can we escape this punishment
and return to God’s favor?
A12. God requires that his justice be satisfied.
Therefore the claims of this justice
must be paid in full,
either by ourselves or by another.
Q13. Can we make this payment ourselves?
A13. Certainly not.
Actually, we increase our debt every day.
Q14. Can another creature—any at all—
pay this debt for us?
To begin with,
God will not punish any other creature
for what a human is guilty of.
no mere creature can bear the weight
of God’s eternal wrath against sin
and deliver others from it.
Q15. What kind of mediator and deliverer
should we look for then?
A15. One who is a true and righteous human,
yet more powerful than all creatures,
that is, one who is also true God.