AC 3471 - Why is there grief first?

AC 3471
The reason why there was grief at first,
is that when truths are being inserted into natural good,
they at first cause pain,
for they oppress the conscience,
and induce anxieties,
because there are concupiscences (lust or cravings) present,
against which spiritual truth combats;
but this first grief by degrees diminishes,
and at last vanishes away.
It is as with a weak and sickly body,
which is to be restored to health by painful means;
in this state, at first it has grief.