Albert Barnes on Matthew 26:12

She did it for my burial. It is not to be supposed that Mary understood clearly that he was then about to die, for the apostles, it seems, did not fully comprehend it, or that she intended it for his burial; but she had done it as an act of kindness and love, to show her regard for her Lord. He said that it was a proper preparation for his burial. Anciently, bodies were anointed and embalmed for the purpose of the sepulchre. Jesus said that this was really a preparation for that burial, as fitting him in a proper manner for the tomb.