Of course it was good for the priest to show mercy instead of law to feed the hungry David with the temple shewbread.
The LORD delights in mercy and compassion.
But it was still
unlawful to do so.
Which is what I have been saying all along ----- that disobeying the letter of the law was not always the wrong thing to do.
Matthew 12:4 KJV
(4) How he entered into the house of God, and did eat the shewbread, which was not lawful for him to eat, neither for them which were with him, but only for the priests?
Which is what I perceive that the OP was trying to ask ........ If you insist on the letter of the law being enforced, where is mercy?
I don't think the line to cross from law to mercy has an iron clad check list, but is an individual heart issue that each must decide for themselves, making the the line of balancing law and mercy different for one from another.
For scripture does tell us that a man is judged as he judges others.
Those that judge harshly will be judged harshly, and those that show mercy will be shown mercy.
Blessed are the merciful for they will be shown mercy.