The reason is because Sunday is the day of the Resurrection of Christ. As “the first day of the week” (Mark16:2) it recalls the first creation; and as the “eighth day”, which follows the sabbath, it symbolizes the new creation ushered in by the Resurrection of Christ. Thus, it has become for Christians the first of all days and of all feasts. It is theday of the Lordin which he with his Passover fulfilled the spiritual truth of the Jewish Sabbath and proclaimed man’s eternal rest in God.
Veja este tema no Catecismo
Paragraph 2174
2174. Jesus rose from the dead "on the first day of the week."104Because it is the "first day," the day of Christ's Resurrection recalls the first creation. Because it is the "eighth day" following the sabbath,105it symbolizes the new creation ushered in by Christ's Resurrection. For Christians it has become the first of all days, the first of all feasts, the Lord's Day (he kuriake hemera, dies dominica) 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.106
Paragraph 2175
2175. Sunday is expressly distinguished from the sabbath which it follows chronologically every week; for Christians its ceremonial observance replaces that of the sabbath. In Christ's Passover, Sunday fulfills the spiritual truth of the Jewish sabbath and announces man's eternal rest in God. For worship under the Law prepared for the mystery of Christ, and what was done there prefigured some aspects of Christ:107
Those who lived according to the old order of things have come to a new hope, no longer keeping the sabbath, but the Lord's Day, in which our life is blessed by him and by his death.108
Paragraph 2176
2176. The celebration of Sunday observes the moral commandment inscribed by nature in the human heart to render to God an outward, visible, public, and regular worship "as a sign of his universal beneficence to all."109Sunday worship fulfills the moral command of the Old Covenant, taking up its rhythm and spirit in the weekly celebration of the Creator and Redeemer of his people.
Paragraph 2190
2190. The sabbath, which represented the completion of the first creation, has been replaced by Sunday which recalls the new creation inaugurated by the Resurrection of Christ.
Paragraph 2191
2191. The Church celebrates the day of Christ's Resurrection on the "eighth day," Sunday, which is rightly called the Lord's Day (cf SC 106).
Acesse nossos estudos biblicos:
How is God’s sovereignty portrayed amidst the chaos in Lamentations 2:8-9?
Jacob’s Wrestle with God: What is the significance of this story for us today?
How important is Jesus’ resurrection, and what can we learn from his appearance to the disciples?
Understanding God’s Wrath – Habakkuk 1:2-4
What does Titus 2:7-8 teach about the standard of conduct for the church?
The Tower of Babel: What Does This Story Teach Us About God’s Sovereignty? (Genesis 11:1-9)
O que o livro de Cantares nos ensina sobre a beleza da mulher noiva e da mulher madura?
