Biblical explanation
John writes: "I was in the Spirit on the Lord's day." Revelation 1:10 Some interpret this as Sunday because of later Christian usage. Others understand it as referring to the seventh-day Sabbath or to the eschatological "day of the Lord." The important point is that Revelation 1:10 does not say: "I was in the Spirit on Sunday." Nor does it explicitly say: "I was in the Spirit on the seventh-day Sabbath." The phrase must therefore be interpreted from Scripture as a whole. Jesus specifically called Himself: "Lord also of the sabbath." Mark 2:28 This provides an explicit biblical connection between Jesus and the Sabbath. The Bible uses the expression "Lord's day" only in Revelation 1:10. It does not explicitly define the phrase as Sunday.
Key takeaway
The great controversy reveals God's character as Christ ministers as our High Priest in the heavenly sanctuary. The dead await the resurrection, Christ's return will be visible and personal, and prophecy calls believers to faithful mission rather than date-setting or fear.