This verse seems to have two separate and unrelated wise sayings. The first mentions “sin,” which we all do. We need to have it “atoned.” The “love and faithfulness” necessary for my atonement would not be my own, but that which is offered by others. Eternally and spiritually, it is God’s love and faithfulness that addresses our sin. But in our daily interpersonal relationships, it is the love and faithfulness of others that atones for our sins and shortcomings.
While the first line deals with sins we have already committed, the second talks about the empowerment to not sin in the future. “The fear of the LORD” is the spiritual insight to see and understand God as He really is. Really seeing all God is, all He can do for us and how much He loves us should motivate us to turn our will and lives over to Him. Both curative (first half) and preventive (second half), this verse addresses all we need for our daily spiritual walk.