Here is a chapter on "The Sabbath" from David Goldstein's book, "LETTERS: Hebrew-Catholic to Mr. Isaacs" (1943). This is valuable to understand because there are certain anti-Catholic sects which denounce the Catholic Church for observing the Lord's Day on a Sunday. This is done without realizing that there are certain things commanded by divine law which Christ's Church can particularize using the authority which was given to it. One such example is seen where by divine law we are all commanded to do some penance for our sins and the Church has further traditionally determined the bare minimum or penance necessary by commanding all Catholics to observe certain days of fast and abstinence.
The designation of Sunday as the Lord's Day is just such a law the Church has made in keeping with the divine law that demands we set apart at least one day, every seven days, to be dedicated to the Lord. The excellent article below explains this subject in detail.

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Following the practice quite common among persons unfavorable to things Catholic, you utterly disregard the answer I made to your assumption, that the mentality of Catholics is submerged by the acceptance of Catholic belief upon authority, and launch forth on some incidental point that is entirely off the compass.
The subject of my last letter was faith. I tried to get you to realize how natural and necessary it is to have faith, even in purely human affairs; how impossible it is to go through life without depending upon authority for knowledge and guidance; how the principle applies to affairs of a supernatural character; how Catholic faith, resting, as it does upon infallible truth, cannot conflict with reason. This is your response,

"You said that `Jesus came to fulfill the Law, and not to destroy it.' How can you reconcile that with changing the Sabbath from Saturday to Sunday? I am prompted to ask this by your statement, just received, that the Commandment to `Keep the Sabbath holy' came by revelation from God, and that it is `binding upon mankind for all time.' To me that is a contradiction."

Perhaps my dissertation upon faith was not entirely in vain, even though you side-stepped the issue. It may have brought you to the realization that there is no use arguing against the inevitable, the use of faith as a guide through life, and to an eternity with God as well. That may be the reason for being silent regarding what I said about faith. Never mind, I will show (with apology to Henry Carey) why

Of all the days that's in the week
Christians love but one day.
And that's the day that comes betwixt
A Saturday and Monday.

It will be easy to prove that what appears to you to be a contradiction, is not a contradiction at all. The Sabbatical Commandment is eternal, as are the other nine Commandments, therefore, Jesus, though "Lord of the Sabbath," did not change it, nor did His Church do so, as you will soon see, I hope. Hence, the question of the Messiah fulfilling, and not destroying the Law, which I will deal with in my next letter, is not affected by the change of the Sabbath Day.
The mandatory declaration of God, "Thou shalt keep the Sabbath holy," is so strongly insisted upon by the Catholic Church, that she, voicing the command of God, insists that her children must go to Church every seventh day, every Sunday, and take part in the highest form of public worship, uniting with the priest in offering Sacrifice to God.
"Ah! but Sunday is not the Sabbath Day," you are likely to say, if you know not, as you seem not to know, what the word sabbath means. It does not mean Saturday, though Saturday has so long been recognized as the Jewish Sabbath day, that the real meaning of the word sabbath has been lost sight of by a multitude of persons. Besides, Sunday being called the "Lord's Day," many persons are unmindful of the fact that Sunday is as much God's Sabbath Day now, as Saturday was in pre-Christian times. God never said, "thou shalt keep Saturday holy." No day of the week bore the name of Saturday at the time when Moses brought the Commandments of God to the children of Israel, nor during a thousand and more years after that wonderful historic occasion. The Jews in the days of Moses counted the days by numbers up to six, and named the seventh day the Sabbath, for God said,

"The seventh day is the Sabbath (the rest day) of the Lord thy God..." (Exod. 20:10).

The word sabbath, in Hebrew Shabbath, means rest, and not Saturday. Hence the Sabbath Day is the day of rest, of ceasing work and giving special homage to God. There are other sabbaths, periods of rest, than the seventh day mentioned in the Old Testament that used to be held sacred by the Jews. For instance, the Mosaic code commands Israel to sow and reap for six years, and to let the land rest during the seventh year. It is called the Sabbatical Year (Exod. 23:10-11; Levit. 25). The year that followed seven sabbatical years was called the Jubilee Year, when slaves were freed, when debts were canceled.
The day part of the Commandment, the seventh day, is held by the Catholic Church to be an unchangeable command. It is the Sabbath of all mankind, and not of the Jews only. No change has been made in it by the Church. What was changed is the point of reckoning the weekly ceremonial day, which is devoted to the Lord God. God did not give Moses a calendar, and say, "Here is where I want the counting of the days to begin." No, God left that for His authorized agents to determine. The day on which the counting of the seven days began is immaterial, provided the selection was made by an authority that functioned by divine will. Moses could speak for the Jews, as Jesus spoke for the Christians, though Jesus spoke through His Church, commissioned by Him to teach whatsoever He willed to be taught, promising to bind in heaven whatsoever it bound on earth (St. Matt. 16; 28).
The Sabbath Day was Saturday during the lifetime of Jesus in Palestine. Being a Jew, the Jewish religion being the only religion of God, Jesus kept the Jewish Sabbath. The Sunday Sabbath did not begin until the Church Jesus established began its work, and even then, for a time, the Saturday was observed by Jewish converts though they also celebrated the first day of the week, assembling for the "Breaking of Bread" (later called the Mass), noted in Acts 2:42; 20:7. It was confusing until the Council of Jerusalem, in A.D. 49, declared officially that the Jewish ceremonial law is not binding upon Christians, though it had automatically come to an end with the practice of the requirements of the New Law.
While the Sabbath Day had to be according to Jewish and later Christian reckoning, the question of the specific day to be observed was always of secondary import, when compared with the obligation to give one day in seven to God in a special way, which is the heart of the Commandment. This must naturally be so, because there never can be a Saturday or Sunday during the same twenty-four hours in all parts of the world at once. Yet all peoples, in all places, can "keep the Sabbath holy," by giving one day in seven to God, though they cannot do so in all parts of the world at the time we go to Church in Boston.
Whether the days are measured by lunar or solar time, the reckoning must change, as the moon and sun changes in relation to each of the four quarters of the earth in which man abides. This was brought forcibly to the attention of the people who listened, during the war in the Pacific, to the news broadcasted by the commentators. They heard on Sundays of battles going on during Mondays, on Fridays to the sinking of vessels on Saturdays. The change in time was strikingly noticeable for the first time to many of the soldiers, marines and passengers when they passed the International Date Line during the war with Japan. When going from east to west Sunday became Saturday in an instant; while traveling from west to east, Sunday became Monday. It was like the changes of an hour in time three times when traveling from New York to San Francisco, when changes are made from Eastern, to Central, to Mountain, and then to Pacific time. Hence, while sailing the Pacific, if a Jew, traveling to Australia happened to pass the Date Line just at sunset Friday he would find himself deprived of his Sabbath, as it would be sunset time of Saturday, when the Jewish Sabbath is at an end. If a Christian, going from Wake Island to Hawaii, were to pass the date line at 12:01 A.M. Saturday, he would find himself with two Sunday Sabbaths in seven twenty-four hour periods. This emphasizes the fact that the change made by the Catholic Church from Saturday to Sunday, as the Sabbath Day, was merely a change in the ceremonial day, without affecting the vital principle in the Commandment, to keep the rest day holy.
Yet the change from Saturday to Sunday is of religious import. It demonstrates the fact that the emphasis of Christianity is far more on the super-natural side of God's law than Judaism ever was. Israel kept holy the Sabbath Day for natural reasons; Christianity celebrates the Sabbath Day for purely super-natural reasons. The Jewish Sabbath was based upon God having made the world in six days, and resting on the seventh (Exod. 20:11). Also in remembrance of God having freed the Israelites from Egyptian bondage (Deut. 5:15). The Christian Sabbath is celebrated on the first day of the week because the Saviour rose from the dead on that day, after atoning for the sin of man, by offering Himself for a redemption, and thus reconciling man with God. Also because it was on the first day of the week that the Holy Spirit, promised by Jesus the Messiah, came down upon the Apostles, when (on that same day) the work of the new, the spiritual creation, the Kingdom of God, the Church of the Messiah, began its work for the salvation of souls (Acts 2).
If the change of the rest day from Saturday to Sunday were an abrogation of the Commandment, to "keep the Sabbath holy," then would the claim that the Law was not destroyed, but fulfilled by the Messiah be a contradiction. But the Commandment stands unimpaired by the change, as the forgoing argument proves, I hope to your satisfaction.
Thus the Lord's Day, the Sabbath Day, is God's Day. It is the Messianic Sabbatical ceremonial day, that has displaced the Mosaic sabbatical ceremonial day, as truly as Christianity has displaced Judaism as the religion of God.
Therefore, we may hail it in the words of Longfellow,

"O day of rest! How beautiful and fair
How welcome to the weary and the old!
Day of the Lord! and truce to earthly care!
Day of the Lord, as all our days should be!"