The Sunday Sabbath is not a law that was only to be observed during the Church Age. In fact, the Sunday Sabbath law was first given on the day Jesus rose from the dead--before the Church Age even began: Matthew 28: 1 In the end of the sabbath, as it began to dawn toward the first day of the week, came Mary Magdalene and the other Mary to see the sepulchre. The original Greek literally reads: "In the end of the sabbaths (plural), as it began to dawn into the first of the sabbaths (plural)..." Early that Sunday morning, at the point of Jesus' rising from the dead, God instituted the Sunday Sabbath. It would still be several weeks before the day of Pentecost and the official beginning of the Church Age, as the Holy Spirit would be poured out on that day and three thousand saved. Therefore, the institution of the Sunday Sabbath day occurred BEFORE the official beginning of the Church Age. And since the Sunday Sabbath day predates the Church Age, there is no reason to think that it comes to an end at the end of the Church Age. The Sunday Sabbath is still in full force today.
Isaiah 58:13 If thou turn away thy foot from the sabbath, from doing thy pleasure on my holy day; and call the sabbath a delight, the holy of the LORD, honourable; and shalt honour him, not doing thine own ways, nor finding thine own pleasure, nor speaking thine own words:
14 Then shalt thou delight thyself in the LORD; and I will cause thee to ride upon the high places of the earth, and feed thee with the heritage of Jacob thy father: for the mouth of the LORD hath spoken it.