Let them, then, laugh a little -.for they will weep a lot in return for what they have earned.

Let them laugh a little: much will they weep: a recompense for the (evil) that they do.

Then let them laugh a little: they will weep much, as the reward of what they used to earn.

Then let them laugh a little and weep much -- a recompense for what they earned.

So let them laugh a little and [then] weep much as recompense for what they used to earn.