Martha's confession in John 11 is second only to Peter's, in the same book. But here in Luke she has something to learn. After a good welcome for Christ and twelve guests, things become more iffy. Mary sits with the Lord to listen to Him, but Martha wants kitchen help (understandably so!). She appeals to Christ, not to Mary - she even blames and gives orders to Him! Let Jesus be Jesus.
He corrects her: one thing is necessary. And Mary's got it. The correction is comparatively mild, as to a younger child. "Don't be troubled! I am the Host; you are the guest." The good thing is the word of the Lord; it gives life, salvation, and forgiveness of sins. We are saved by this Word, not by works according to the Law. Works of the saved are good, but the good thing is the Word.
This story is not about church work. It's about attending to the Word, the one thing that justifies you before God. So be like Mary - sit down and listen to Him.
Soli Deo gloria.