The Jews knew that even when Messiah comes, there will still be the poor in the land as noted by the following.

“there is no difference between this world (this present time) and the times of the Messiah, but the subduing of kingdoms only; as it is said, (Deut 15:11), “for the poor shall never cease out of the land”: the gloss on it is, from hence it may be concluded, that therefore, “for ever there will be poverty, and riches”.”  (T. Bab. Sabbat, fol. 63. 1 qt’d in Gill)

Deuteronomy 15:11  There will always be poor people in the land. Therefore I command you to be open-handed towards your brothers and towards the poor and needy in your land.

Here is the essence of what Jesus is saying: some things we can do any time, but other things must be done when the opportunity arises, or it may be lost. Don’t miss the opportunities that present themselves to you.

Martha and Mary were sisters, both in blood and in their relationship with Christ and yet their service to Him was vastly different. Martha was the quiet, behind the scenes person who served Jesus by working in the kitchen fixing and serving the meal; Mary was the highly visible sister who served Jesus by pouring out her love through her emotions. At one time Martha had become frustrated because Mary wasn’t serving as she was and undoubtedly Mary looked down on her sister because she wasn’t as outgoing in her expressions of love to Christ as she, but Jesus would have nothing of this. God made us different on purpose and we are to serve Him in different ways using those gifts he has individually given to us (1Cor 12:5). We should never, ever consider ourselves better than someone else just because we serve God in a different manner.

1 Corinthians 12:5  There are different kinds of service, but the same Lord.

In the other gospels (Mat 26:13, Mark 14:9) Jesus makes a promise about “this woman” but Mary remains unnamed in both. Here in John we learn her name but do not hear of the promise. It doesn’t matter if you receive recognition for the things you do for God or if you are given a promise because of them. The only thing that really matters is whether you touch the heart of Jesus. That is the sole rule by which you should judge the service or the worship you do for the Lord. Did you bless His heart?

Matthew 26:13  I tell you the truth, wherever this gospel is preached throughout the world, what she has done will also be told, in memory of her.”

Mark 14:9  I tell you the truth, wherever the gospel is preached throughout the world, what she has done will also be told, in memory of her.”

John didn’t answer their question directly. Note that he did not even consider himself worthy to unloose the sandal of Jesus, the most menial of tasks, which was only performed by a slave.  According to Barclay one Rabbinic saying states that a disciple may do for his master anything that a servant did except to untie his sandals. This function was too menial for even a disciple to do. As Morris says, “Humility could scarcely take a lower place.” (NICNT 141)

Christians vary in many ways. They have different gifts, different knowledge, and a variety of character traits. No two of us are alike and yet every Christian who is great in the eyes of the Lord has one trait in common — humility. John was a great example to us of what a man or woman of God should be like and how they should think of themselves. His opinion of himself was that he was unworthy to do the most menial of tasks for Christ and yet Jesus said of him that he was a shining light (John 5:35) and that there were none greater among men (Matt 11:11). We need to follow his example and clothe ourselves with humility (1 Peter 5:5).

John 5:35  John was a lamp that burned and gave light, and you chose for a time to enjoy his light.

Matthew 11:11  I tell you the truth: Among those born of women there has not risen anyone greater than John the Baptist; yet he who is least in the kingdom of heaven is greater than he.

1 Peter 5:5  Young men, in the same way be submissive to those who are older. All of you, clothe yourselves with humility towards one another, because, “God opposes the proud but gives grace to the humble.”