The master violated the covenant he had sworn to keep by taking advantage of the servant girl. The Lord required the man to present a ram as a guilt offering to the priest. The ritual for the guilt offering would be performed by the priest, thus making atonement for sin. This law shows that not only free Israelites were regarded and protected, but vulnerable slave girls as well.
21 but he shall bring his compensation to the LORD, to the entrance of the tent of meeting, a ram for a guilt offering.