Romans 14:6

ὁ φρονῶν τὴν ἡμ. Cf. Romans 8:5; Philippians 3:19; Colossians 3:2; Mark 8:33 (|[275] Mt.).

[275] | parallel to

κυρίῳ φρονεῖ. Dat. to denote the person whose interest is affected, Blass p. 111. Anarthrous κύριος is used (1) after O.T. as a name for GOD, passim. (2) of Christ, very rarely without the addition of Ἰ. or Χρ. or both: and then only with a preposition (2 Corinthians 11:17; Ephesians 6:8 = Colossians 3:20 (?); 1 Thessalonians 5:17) or in gen. after anarthrous subst. (1 Corinthians 7:25; 1 Thessalonians 4:15; 2 Timothy 2:24). There is no clear parallel to the use in this passage if we take κ. as = the Lord Christ.

So tr. to a master: he has a master to whom he is responsible and in view of whom he forms his opinion; the master is Christ. See next verse.