Two classes exist for repairing faults, and no ancient source explains the difference between them in terms a modern reader finds sufficient. Both are brought for wrongs, both involve a priest, and in several passages they appear together for a single occasion. Where the boundary runs is a genuine scholarly dispute rather than an obscurity that better manuscripts would clear up.
One position takes the distinction to be about what has been damaged. The purification offering addresses contamination of the sacred precinct; the reparation offering addresses an encroachment on what belongs to the sanctuary or, by extension, an oath that has profaned the divine name, and its remedy is compensatory because the damage is quantifiable. On this reading the two are complementary and the reparation offering is essentially a penalty payment with a rite attached. A second position reads the reparation offering as the older and looser category, absorbed unevenly into the Priestly system, and treats the overlaps as evidence of that history rather than of a design.
Several concrete differences survive whichever way the question is answered. The reparation offering is always a ram and never varies with the offerer's means, where the purification offering has a scale running from a bull to a measure of flour. Its blood is dashed against the sides of the altar rather than placed on the horns. And it is the only class that is valued in silver before it is brought, so that a person could in principle bring the money and buy the animal at the sanctuary.