What does Mark 14:6 mean?

While he was at Bethany, in the house of Simon the leper, as he sat at the table, a woman came having an alabaster jar of ointment of pure nard—very costly. She broke the jar, and poured it over his head.

But there were some who were indignant among themselves, saying, “Why has this ointment been wasted?

For this might have been sold for more than three hundred denarii, and given to the poor.” They grumbled against her.

For you always have the poor with you, and whenever you want to, you can do them good; but you will not always have me.

She has done what she could. She has anointed my body beforehand for the burying.

Most certainly I tell you, wherever this Good News may be preached throughout the whole world, that which this woman has done will also be spoken of for a memorial of her.”