What does Matthew 26:10 mean?

The disciples have not been impressed by a woman's extravagant act of devotion and worship. She has opened an enormously-expensive bottle of perfumed oil and has poured it all over Jesus' head. If John 12:1–11 tells the same story, the perfume was worth nearly as much as a year's wages and the woman poured it over Jesus' feet, as well.

The disciples condemned the woman for this, at least to each other. Why not sell that expensive bottle of oil and give all the money to the poor? Why seemingly waste it, anointing Jesus in this outrageous way?

Jesus, though, knows what they're thinking and saying to each other. He rebukes them and uses a question to tell them to leave the woman alone. Jesus describes her extravagant act of devotion as a beautiful thing. He will show that in pouring this oil over Him, this woman has begun to prepare Him for the burial that will follow the brutal events of the coming days, something the disciples still don't seem to grasp.