In Old Testament times, when the Sabbath was in force, it was not OK. In fact, when Nehemiah was governor of Jerusalem he forbade selling on the Sabbath and even threatened to attack people who came to Jerusalem to sell on the Sabbath after he had forbidden it:
15 In those days I saw in Judah people treading winepresses on the Sabbath, and bringing in heaps of grain and loading them on donkeys, and also wine, grapes, figs, and all kinds of loads, which they brought into Jerusalem on the Sabbath day. And I warned them on the day when they sold food. 16 Tyrians also, who lived in the city, brought in fish and all kinds of goods and sold them on the Sabbath to the people of Judah, in Jerusalem itself! 17 Then I confronted the nobles of Judah and said to them, “What is this evil thing that you are doing, profaning the Sabbath day? 18 Did not your fathers act in this way, and did not our God bring all this disaster on us and on this city? Now you are bringing more wrath on Israel by profaning the Sabbath.” (Nehemiah 13:15-18)
His reason for this was because it was against God’s command and was going to take the people away from God. However, in the New Testament there is no explicit command to keep the Sabbath in this way. Instead, there are principles which should guide us in how we use all of our time:
5 One person esteems one day as better than another, while another esteems all days alike. Each one should be fully convinced in his own mind. 6 The one who observes the day, observes it in honor of the Lord. The one who eats, eats in honor of the Lord, since he gives thanks to God, while the one who abstains, abstains in honor of the Lord and gives thanks to God. (Romans 14:5-6)
So, whatever we choose to do, we have to be convinced it is the right thing for us to do. If we choose to keep aside one day for God as particularly special (like the Sabbath) then we should keep that day in honor of the Lord. If we choose to view all of our days as special because they have all been given to us by God, then that is what we should do. If we think that we should not buy food on a particular day because that day is special to the Lord (or even not eat food), then we should not buy food on that day. If we think the food is given to us by God and we give thanks for it, then buying and eating it is fine on any day of the week. We just have to be convinced that we do the right thing.
Verses 7 – 9 tell us that the important thing is that we recognise that we are the Lord’s because he died and was resurrected to be our Lord, and that we live for him in everything that we do. If the things we do on the Sabbath (or any other day) are taking us away from him, like they were in the time of Nehemiah, then we should consider changing them to make sure that we do live for him in everything.