When Christ is discussing salvation with the rich young ruler, elaborating upon which commands to keep to secure eternal life, He lists several from the Decalogue yet mixes in, “Defraud not” (Mk 10:19), which is unexpected.
Torah does contain this command (Le 19:13), but it isn’t one we’d expect Christ to highlight. From context, since Christ is evidently listing commands which relate to how we treat our fellow Man, this might be a reference to the 10th commandment, “Thou shalt not covet.” But if so, why does He reference it this way?
Interestingly, when Luke recounts this same story there’s no reference to this concept at all (Lk 18:20), and Matthew (Mt 19:18-19) replaces it with the 2nd Great Command (Mk 12:31), summarizing the entire horizontal dimension of Torah. (Ro 13:9) What do we make of this?
If we ponder Thou shalt not covet, we might find it includes Defraud not: coveting leads to defrauding – inappropriate wanting tends to wrongful dispossession. Both concepts violate the law of Love, so including love thy neighbor as thyself as a capstone is reasonable. Perhaps Christ hints that this man’s wealth was fraudulently obtained (Ja 5:4), hence the remedy in returning it. (Mk 10:21) Such a cure for the burden of wealth is by no means universal (1Ti 6:16-8), so we’d expect circumstance to motivate His invitation here.
What the variations of this story reinforce is that covetousness and lust are necessarily a matter of defrauding another, violating the law of love. It isn’t wrong to strongly desire what’s lawfully obtained (De 14:26), or to enjoy the inherent goodness of God’s design in Creation. (Tit 1:15) But if we leave another unjustly the worse in obtaining our desire, we should prayerfully reconsider.