ISB ~ Romans 14 v5

one day as better:Refers to the sacred days of the Old Covenant calendar, including the weekly Sabbath. These ceremonial times belonged to the Mosaic age that expired with the coming of the messianic age (Gal 4:10; Col 2:16). For this reason, they are not binding on the Christian conscience, although Jewish converts are still permitted to observe them in the earliest days of the Church. Note that Paul is not indifferent to holy days as such, but only to the ritual feast days of Judaism. See note on Acts 21:21.