Mary sat at Jesus’ feet and listened to His teaching. The one thing necessary is continued catechesis—continued learning and growing in the Word of Christ. This is what Mary was doing.
In Luke 1:4 we are informed that the Gospel was written so that the unidentified Theophilus would have certainty concerning the things that he was “taught” (literally “catechized”). Theophilus, Mary, Martha and each “mature” Christian has been catechized—taught the foundational truths of the faith. Jesus would drive home the reality that the one thing necessary is to continue at His feet, continue to be catechized. Was Martha’s work of serving then worthless? By no means! But continued catechesis is the ultimate necessity.
Such continued catechesis should first be realized in the home. Upon completion of the 8th grade when children are traditionally “confirmed” among us, they may wrongly be given the impression that they are done, that they have “graduated”. The head of a given household should take it upon himself to keep his family at the feet of Jesus. We then also should take it upon ourselves to have Jesus continue catechizing us as individually we daily study our catechism. Martin Luther, who penned the Small Catechism, wrote in his preface to the Large Catechism: “I must still read and study the [Small] Catechism daily, yet I cannot master it as I wish, but must remain a child and pupil of the Catechism…” Luther remained at the feet of Jesus, he remained a student of the Catechism. Of course “catechesis” generally connotes instruction in God’s Word, but specifically it refers to instruction drawn from The Small Catechism.
Some might ask, “Why are you emphasizing The Small Catechism? Shouldn’t our emphasis be upon continued study of the Bible?” Truly we, unlike most in previous centuries, are privileged to personally own and be able freely to study the Holy Bible, the fountain of all doctrine. This is wonderful, yet, as is true of any difficult and deep subject, one must first master the basics, the framework. Thus to find your way around a city you must first learn the main roads. Using the main roads you will then learn various roads that branch off of these thoroughfares. The Small Catechism is a wonderful condensation of Holy Scripture, conveying the “main roads” of the faith. What better way to learn the depths of the Holy Bible than to first master its “main roads”. Yet as Luther rightly reminds, in this sinful world no one fully masters even the basics of the faith. So remain a catechist at the feet of Jesus.
Even as The Small Catechism is a wonderful condensation of the entire Bible, so there is an even more concentrated condensation. The one-word condensation of the Catechism is the same as the one-word condensation of the entire Bible: Jesus. Jesus—crucified and risen—is the meaning behind, the fulfillment of, and the direction taken in each of the six Chief Parts of the Catechism. Jesus—crucified and risen—is the summary of the entire Bible (John 5:39, etc.). Indeed, we sit at the feet of Jesus that we may learn not only from Jesus, but about Him. And through that Word the Holy Spirit brings eternal gifts, gifts wrought by Jesus.
 Luther notes that the church through the centuries especially recognized the first three chief parts to be foundational (Decalogue, Apostles’ Creed, Lord’s Prayer).