John 12:3 - 12:8
12:3 Then took Mary a pound of ointment of spikenard, very costly, and anointed the feet of Jesus, and wiped his feet with her hair: and the house was filled with the odour of the ointment.
12:4 Then saith one of his disciples, Judas Iscariot, Simon's son, which should betray him,
12:5 Why was not this ointment sold for three hundred pence, and given to the poor?
12:6 This he said, not that he cared for the poor; but because he was a thief, and had the bag, and bare what was put therein.
12:7 Then said Jesus, Let her alone: against the day of my burying hath she kept this.
12:8 For the poor always ye have with you; but me ye have not always.
So, Mary wastes expensive ointment on Jesus' feet, rather than selling the ointment and giving the money to the poor. But Jesus thinks his feet are more important, saying that poor people will always be around, but he and his precious feet won't be. (According to the New Oxford Annotated Bible, 300 denarii would be nearly a year's wage for a laborer.
Now it turns out that it wouldn't have gone to the poor, but apparently Jesus didn't know that. At least he gives a different reason for wanting the ointment for himself.
And... won't we have Jesus always? That's what everyone says, that he is here with us always.
And... here Jesus acknowledges that there will always be poor people in spite of his glory and in spite of his coming back to earth after his death... which of course, he knew would happen.