Understand that 'reap the harvest' implies a direct result of previous actions, good or bad.

Causal Link

'Reaping the harvest' is often used metaphorically, not involving actual farming.

Metaphorical Usage

The phrase can have a positive spin (rewards) or a negative one (consequences).

Literally refers to the act of gathering crops, usually at the end of the growing season.

Used in a farming or gardening context when talking about physically harvesting crops.

Unlike the idiomatic usage, it can be used literally to talk about actual harvest seasons.