The Commandments speak of remembering the Sabbath day and keeping it holy (Gen. 2, 3; Exodus. 20, . The Sabbath is Saturday, so why do Catholics worship publicly on the first day of the week, that is, Sunday?”
This is a question normally posed by those – such as the Seventh Day Adventists – who regard Sunday worship as a mark of the Apostate Church of the Beast. Our Lord Jesus Christ declared that He was Lord of the Sabbath and that its observance was at His disposal: St. Matt. 12, 1-8; St Mark 2, 24-26; St. Luke 6, 5; St. John 5, 10-11. As a consequence, the early Church, in order to distinguish itself from the worship of the Synagogue, felt itself free from to depart from Sabbath worship and worship God on an alternate day of the week. This is evident from the words of St. Paul to the Colossians: “Therefore do not let anyone condemn you in matters of food and drink or of observing festivals, new moons, or Sabbaths. These are only a shadow of what is to come, but the substance belongs to Christ” (2, 16-17). If Christ Himself had the power to “dispose” of the Sabbath, so too His Church which is His Body.
To read more on this topic and other catholic related issues,go to:www.catholicteachings-mikkyijege.blogsport.com

Jesus didnt take away the sabbath but rather came to fulfil it. Sabbath means rest. The primary purpose of sabbath was not worship but to rest. Jesus is lord of sabbath ( rest)

Matthew 11:28
Come unto me, all ye that labour and are heavy laden, and I will give you rest.

When a man recieves Christ ,by faith he has entered into rest.

Hebrews 4:10
For he that is entered into his rest, he also hath ceased from his own works, as God did from his.

But as regards worship ,theres no special day any longer,of course the early church meet on sunday. Jesus didnt give any command on such. but we all generally accepted it for formalty sake and its good. but our wowrship of God is not limited to a special day.The real sabbath is life in christ. christ in you.

Col. 2:16
Let no man therefore judge you in meat, or in drink, or in respect of an holyday, or of the new moon, or of the sabbath days:

Does that mean I dont have to go to church? Since Sunday service is "illegal"?

Any one is ok. Whether it is Sunday, Monday Friday or whenever. What is important is that you have a personal relationship with your creator!

mabell:

Does that mean I dont have to go to church? Since Sunday service is "illegal"?

Please oo, I should not be misunderstood. God is not against our sunday worship. Jesus recognised that christians meet on sundays to honour him. If he had any issues ,he would have told them. He appeared to them at least twice when they were gathered for worship on sunday

Hebrews 10:25
Not forsaking the assembling of ourselves together, as the manner of some is; but exhorting one another: and so much the more, as ye see the day approaching.

Joagbaje:

Please oo, I should not be misunderstood. God is not against our sunday worship. Jesus recognised that christians meet on sundays to honour him. If he had any issues ,he would have told them. [size=15pt]He appeared to them at least twice when they were gathered for worship on sunday[/size]

How do you mean?

They were gathered on sunday when Jesus appeared to them,thomas was missing

John 20:19
Then the same day at evening, being the first day of the week, when the doors were shut where the disciples were assembled for fear of the Jews, came Jesus and stood in the midst, and saith unto them, Peace be unto you.
The second sunday they were gathered again and he still came.

John 20:26
And after eight days again his disciples were within, and Thomas with them: then came Jesus, the doors being shut, and stood in the midst, and said, Peace be unto you.

And other account by apostles also confirm sunday worship

Acts 20:7
And upon the first day of the week, when the disciples came together to break bread, Paul preached unto them, ready to depart on the morrow; and continued his speech until midnight.

1 Cor. 16:2
Upon the first day of the week let every one of you lay by him in store, as God hath prospered him, that there be no gatherings when I come.