Yes observing the sabbath is crucial ,
Because there is often confusion about this, it should be noted that Catholics do not consider Sunday to be the “sabbath.” Instead, the Catechism of the Catholic Church notes:
“Sunday is expressly distinguished from the sabbath which it follows chronologically every week; for Christians its ceremonial observance replaces that of the sabbath.”
Sunday is considered the Lord’s Day. "For Christians it has become the first of all days, the first of all feasts, the Lord’s Day…Sunday:
We all gather on the day of the sun, for it is the first day [after the Jewish sabbath, but also the first day] when God, separating matter from darkness, made the world; and on this same day Jesus Christ our Savior rose from the dead."–CCC 2174-2176.
Judeo-Christians of the first century observed both the Sabbath (since they were ethnically Jews) as well as the Lord’s Day. “These customs…were kept by Jewish Christians, that is, in a spirit of homage to the divine authority and prophetic holiness of these signs–and not in order to attain salvation.” (St. Bede,
Expositio Actuum Apostolorum) Today there are Hebrew-speaking Catholics in Israel of Jewish ethnicity (
The Association of St. James) who in like manner might observe the “sabbath” and then on the next day observe the Lord’s Day (as do some Hebrew Catholics in other parts of the world).
But not all Christians observe the Lord’s Day. Members of the SDA observe the sabbath and not the Lord’s Day, and the Jehovah’s Witnesses do not observe any day of rest (of course some people have different opinions whether or not these groups are technically Christian).
And some Christians, including some of us Catholics, don’t do a very good job of honoring the Lord’s Day as we should.