The Lord answered her, “Martha, Martha, you are worried and upset about many things, but one thing is necessary. Mary has made the right choice, and it will not be taken away from her.” (Luke 10:41-42 HCSB)
Jesus was travelling and stopped in a village where Martha and Mary lived. They were sisters. Martha welcomed Jesus and the disciples that were travelling with Him and showed much hospitality while Mary sat at Jesus' feet and listened to His teaching. Martha complained to Jesus and asked Him to convince Mary to help. The Lord did not meet her request. Instead, He corrected her.
At first glance this seems to show a lack of appreciation on Jesus' part for Martha's hard work and hospitality. It was not just the Lord she was serving but His entourage as well ("While they were travelling...).
Martha was, "distracted by her many tasks," and, "worried and upset about many things." Perhaps she went above-and-beyond, serving a larger variety of food than was necessary. Perhaps her concern was over how much more she was doing to serve the Lord than Mary, and perhaps she was trying to highlight how hard she was working for the Lord as compared to Mary. There are times to serve and there are times to sit at Jesus' feet and listen to His teaching.
Only God knows the attitude of her heart that was part of her request. But one thing is certain: Whenever we compare ourselves to others we will bring about the Lord's rebuke. If you feel compelled to compare yourself to someone else to highlight how good you are, compare yourself only to the Lord, Jesus Christ.