William Burkitt on Romans 16:5

Three persons are here saluted by name;

the first, Epenetus, whom he calls the first-fruits of Achaia; that is, the first person that embraced Christianity, or the faith of Christ, in the region of Achaia:

the second is Mary, a common name, but the person here intended was of special note, having bestowed much pains upon, and done many good offices for, the preachers of the gospel:

the third is Andronicus, noted for his sufferings and services among the apostles, as also for his early embracing the Christian faith. He was in Christ before me; that is, converted to Christianity before myself.

Learn hence, 1. That seniority in grace is a very great honour; and to be in Christ before others, is a transcendent prerogative.

Learn, 2. That God will have the good works of all his saints, and the services especially which are done to his ministers and ambassadors by any of his people, to be applauded, valued, and recorded. Mary's labour bestowed on the apostle, is here mentioned with respect.