Mary breaks and anoints Jesus with a VERY expensive perfume. What seems like a waste to some was actually Mary could do for Jesus. This came just a couple of months after Jesus had raised her brother Lazarus from the dead. When Mary considered what Jesus had done for her and her family, it was clear what she should do with her jar of perfume that she had been saving. It was the best way she could honor Jesus. In a similar way, when we offer back to God our faith in giving His Son's work - it honors Him. It's a reasonable act of worship in view of God's mercy - (Romans 12:1)