It took God just 6 days to create everything. This is a testimony to His omnipotence.
Genesis 2:1-3 Thus the heavens and the earth were finished, and all the host of them. 2 And on the seventh day God ended his work which he had made; and he rested on the seventh day from all his work which he had made. 3 And God blessed the seventh day, and sanctified it: because that in it he had rested from all his work which God created and made.
That creation was “finished” means that there was no more creation out of nothing (ex nihilo). All physical matter had been created. Of course, the created matter could change through various means (chemical, nuclear, etc.), but from this point, matter could neither be created or destroyed (First Law of Thermodynamics).
God rested in the sense that he ceased from created. It was not because He was tired. It means simply that He stopped because He was done. This is the sense from the phrase, “from all his work which he had made”.
God set apart the seventh day (Saturday) as a special day commemorating His creation. It would become very significant to the nation of Israel as a day in which no work would be done as codified in the 10 Commandments.
Exodus 20:8-11 Remember the sabbath day, to keep it holy. 9 Six days shalt thou labour, and do all thy work: 10 But the seventh day is the sabbath of the LORD thy God: in it thou shalt not do any work, thou, nor thy son, nor thy daughter, thy manservant, nor thy maidservant, nor thy cattle, nor thy stranger that is within thy gates: 11 For in six days the LORD made heaven and earth, the sea, and all that in them is, and rested the seventh day: wherefore the LORD blessed the sabbath day, and hallowed it.
This is the basis for the 6-day workweek. It is also another great argument for taking the days of Genesis 1 as 24-hour days. Our workweek would really strange otherwise.
It should be noted that this “sabbath day” was part of the Law and it is debatable that it is applicable in any way to Christians. Christians certainly do not observe all of the Sabbath constraints. For one thing, many Christians work on Saturday which is punishable by death under the Law (Exodus 31:14-15). Christians also travel on Saturday, which was also forbidden (Exodus 16:29). There are other restrictions as well which Christians do not follow. Some say that Sunday is the “Christian Sabbath”, although I see no basis in Scripture for this. Jesus arose on Sunday and Christians throughout church history have used Sunday as their day of worship. Using Sunday as a “day of rest and worship” is fine, but Christians simply do not practice Sabbath-keeping like the Jews were required to do.
That said, we should never forget that God chose a day of rest to appreciate what He had created. We should note that we also need to take time and cease from our labors and appreciate His creation as well.