Working on Sunday is definitely not a sin. Working on Sunday is not prohibited in the Bible. The idea that Christians should not be working on Sunday comes from a misunderstanding of Old Testament Sabbath-keeping for the Israelites and its relation to Sunday worship for Christians. According to Exodus 20:8–11, the Sabbath is the seventh day of the week, on which the Israelites were to rest, in remembrance that God created the universe in six days and then “rested” on the seventh day. “Keeping the Sabbath holy” was defined as not working on the Sabbath.
When God provided manna in the desert during the Exodus wanderings, He commanded that the manna was to be gathered for six days only with enough gathered on the sixth day to feed the people during the Sabbath rest. Gathering the manna was considered to be work, just as planting and harvesting was considered work. Exodus 31:14–16, 35:2 proscribed death for anyone who worked on the Sabbath. Buying and selling on the Sabbath day was also considered a desecration of the Sabbath (Nehemiah 13:15–17). Clearly, keeping the Sabbath day “holy” required the cessation of all work for the Israelites.
The Sabbath day was established so the Israelites would rest from their labors, only to begin again after a one-day rest. Why, then, do Christians not have to observe the same law? The key to understanding this is to see that the various elements of the Sabbath symbolized the coming of the Messiah, who would fulfill the law by providing a permanent—as opposed to a one-day—rest for His people. With the establishment of the Old Testament Law, the Jews were constantly “laboring” to make themselves acceptable to God. Their labors included trying to obey all the commandments of the ceremonial law, the Temple law, and the sacrificial law. Of course they couldn’t possibly keep all those laws, so God provided an array of sin offerings and sacrifices so they could come to Him for forgiveness and restore fellowship with Him, but only temporarily.
Just as they began their physical labors after a one-day rest, so, too, did they have to continue to offer sacrifices. Hebrews 10:1 tells us that the law “can never, by the same sacrifices repeated endlessly year after year, make perfect those who draw near to worship.” But these sacrifices were offered in anticipation of the ultimate sacrifice of Christ on the cross, who “after He had offered one sacrifice for sins forever, sat down on the right of God” (Hebrews 10:12). Just as He rested after performing the ultimate sacrifice, He sat down and rested—ceased from His labor of atonement because there was nothing more to be done, ever. Because of what He did, we no longer have to “labor” in law-keeping in order to be justified in the sight of God and this includes the observance of the Sabbath. Jesus was sent so that we might rest in God and in what He has provided.
By saying, “The Sabbath was made for man, not man for the Sabbath” (Mark 2:27), Jesus was restating the principle that the Sabbath rest was instituted to relieve man of his labors, just as He came to relieve us of our attempting to achieve salvation by our works. We no longer rest for only one day, but forever cease our laboring to attain God’s favor. Jesus is our rest from works now, just as He is the door to heaven, where we will rest in Him forever. There is no other Sabbath rest besides Jesus. He alone satisfies the requirements of the Law, and He alone provides the sacrifice that atones for sin. He is God’s plan for us to cease from the labor of our own works.
In Colossians 2:16–17, the apostle Paul declares, “Therefore do not let anyone judge you by what you eat or drink, or with regard to a religious festival, a New Moon celebration or a Sabbath day. These are a shadow of the things that were to come; the reality, however, is found in Christ.” We are no longer commanded to cease working on the Sabbath, nor is Sunday now the “Christian Sabbath.” Although many Christians prefer to take Sunday off and spend at least part of it in corporate worship, working on Sunday is not sin. Many Christians, such as doctors and nurses, have no choice but to work on Sunday and, as a society, we should be very grateful to them. But Christians who work on Sunday should do so with the understanding that worship is not limited to any one day of the week, but is to be an ongoing part of their lives.
 Got Questions Ministries. (2010). Got Questions? Bible Questions Answered. Bellingham, WA: Logos Bible Software.