3 The one who eats everything must not despise the one who does not, and the one who abstains must not judge the one who eats everything, for God has accepted him. 4 Who are you to pass judgment on another’s servant? Before his own master he stands or falls. And he will stand, for the Lord is able to make him stand. 5 One person regards one day holier than other days, and another regards them all alike. Each must be fully convinced in his own mind. 6 The one who observes the day does it for the Lord. The one who eats, eats for the Lord because he gives thanks to God, and the one who abstains from eating abstains for the Lord, and he gives thanks to God.
Beitzah 16aBabylonian Talmud
It is taught in a baraita: They said about Shammai the Elder that all his days he would eat in honor of Shabbat. How so? If he found a choice animal, he would say: This is for Shabbat. If he subsequently found another one choicer than it, he would set aside the second for Shabbat and eat the first. He would eat the first to leave the better-quality animal for Shabbat, which continually rendered his eating an act of honoring Shabbat. However, Hillel the Elder had a different trait, that all his actions, including those on a weekday, were for the sake of Heaven, as it is stated: “Blessed be the Lord, day by day; He bears our burden, our God who is our salvation; Selah” (Psalms 68:20), meaning that God gives a blessing for each and every day. That is also taught in a baraita in more general terms: Beit Shammai say: From the first day of the week, Sunday, start preparing already for your Shabbat. And Beit Hillel say: “Blessed be the Lord, day by day.”
Notes and References
"... First of all the parenthesis about 'days' is interesting: 'One distinguishes a certain day above the other, while another distinguishes every day. Let everyone be fully convinced in his own mind: he who observes the day observes it for the Lord ... ' (Rom 14:5-6a). Let us first isolate the clause, '... another distinguishes every day'. The expression is strange, since the very word 'judge' or 'distinguish', implies 'distinction'. It seems to indicate some special intention. This is confirmed by parallels in Rabbinic, pagan Greek and Hellenistic Jewish literature. The Rabbinic parallel features in a controversy, and this is significant ... Shammaites continuously directed their attention towards the sacrosanct seventh day, but Hillel and his school somehow celebrated all the days of the week ..."
Tomson, Peter J. Paul and the Jewish Law: Halakha in the Letters of the Apostle to the Gentiles (p. 246) Fortress Press, 1990