Luke 6:36

The word therefore is carrying an argument, and the argument is in the verses above.

Luke has just recorded the hardest instructions in the Gospels: love your enemies, do good to those who hate you, bless those who curse you, lend expecting nothing back. Then the reason — because God is kind toward the unthankful and evil. And then this verse, which turns the observation into an instruction.

So the standard is not fairness. It is imitation. Be merciful, even as your Father is also merciful. The comparison is not offered as an ideal to approach asymptotically; it is offered as the pattern.

What makes it liveable is where the mercy comes from. This is not an appeal to your reserves of patience, which run out on schedule. It is an instruction to pass on something you have received, and the whole passage assumes you are downstream rather than upstream. You cannot give this out of nothing.

And Matthew records the same line with a different word — be perfect, as your heavenly Father is perfect. Luke's version is more specific and, oddly, more demanding. Perfection is abstract enough to feel distant. Mercy is concrete: it names a person you would rather not forgive, and it is due on Tuesday.