What does John 12:8 mean?

This is the second part of Jesus' defense of Mary, sister of Lazarus. She was criticized by Judas for "wasting" precious oil anointing Jesus, rather than selling it and giving the money to the poor (John 12:1–4). The truth is that Judas was bitter to see a chance at theft slip through his fingers (John 12:5–6). Jesus began His response by noting that Mary's actions relate to His impending death and burial. Though Mary was a student of Jesus (Luke 10:38–42), it's hard to know just how well she understood what was about to happen. Knowingly or not, this was her chance to anoint Jesus body, since she won't be present when the other women approach the tomb after His death (Mark 16:1).

Here, Jesus makes a remark about the poor which can be grossly misunderstood if taken out of context. Judas' complaint was a clever deception because it contained an element of truth. Logically, Mary could have sacrificed her oil for the poor, instead of an anointing. However, the opportunity to honor Jesus was unique—it was the last chance she would have for that act of worship. The symbolism and lesson contained in that act is one that has been preserved in God's own Word (Mark 14:6–11).

Jesus' comment is not, at all, meant to brush aside the idea of caring for those who are poor. Suggesting otherwise means ignoring everything else the Bible says about service, sacrifice, charity, and love (Matthew 5:16; James 1:27). Rather, the point is about the uniqueness of this moment. Seven days from the evening described here, there will still be opportunities to feed the poor of Jerusalem; but Jesus will not be there anymore. Mary isn't "wasting" money on something she could have done at any time or any place. She was inspired to take advantage of a irreplaceable moment in time—and for that, she deserved respect, not derision.