How do we know that Mary’s act was a good work?

Mary's anointing of Jesus with expensive ointment is the only act that Christ explicitly labeled as a good work. In Mark 14:6-9, Jesus defends Mary against the criticism of His disciples, saying that she has done a beautiful thing for Him. This commendation reinforces that true good works stem from a heart motivated by love and faith in Christ. Mary's action was not dictated by obligation, but was spontaneous and sacrificial, driven by her deep love for her Savior. The significance of this act is further cemented by Christ’s promise that it would be remembered wherever the gospel is preached, showcasing its everlasting impact.