Will only those who accept the Sabbath truth be among the Remnant.

When Sunday laws appear, will this show Christians the Sabbath truth so they can choose? What does the SOP tell us concerning the Sabbath, of those who will leave Babylon at the end. With the Pope pushing Sunday worship Sunday worship, what before the Sunday Laws will trigger the understanding of the true Sabbath.

Will all "Christians" keep the Sabbath. No. Will some. Yes.

Re 12:17 And the dragon was wroth with the woman, and went to make war with the remnant of her seed, which keep the commandments of God, and have the testimony of Jesus Christ.

Re 14:12 Here is the patience of the saints: here are they that keep the commandments of God, and the faith of Jesus.

The majority of "Christians" will be keeping Sunday. That will be the rest day enforced by the church/state.
But those who are among the "called, chosen and faithful" following the Lamb, will keep all God's moral law, including the Sabbath.

The lives of God's people. It won't be sermonizing, but, God's Remnant Church living a Christlike life.

Fearful is the issue to which the world is to be brought. The powers of earth, uniting to war against the commandments of God, will decree that no man may buy or sell, save he that has the mark of the beast, and, finally, that whoever refuses to receive the mark shall be put to death. [Revelation 13:15, 17.] The word of God declares: "If any man worship the beast and his image, and receive his mark in his forehead, or in his hand, the same shall drink of the wine of the wrath of God, which is poured out without mixture into the
cup of his indignation." [Revelation 14:9, 10.]

But not one is made to feel the wrath of God until the truth has been brought in contact with his mind and conscience, and has been rejected. There are many in the churches of our country who have never, even in this land of light and knowledge, had an opportunity to hear the special truths for this time. The obligation of the fourth commandment has never been set before them in its true light. Jesus reads every heart, and tries every motive. The decree is not to be urged upon the people blindly. Every one is to have sufficient light to make his decision intelligently. The Sabbath will be the great test of loyalty; for it is the point of truth especially controverted. {4SP 422.2}
Heretofore those who presented the truths of the third message have often been regarded as mere alarmists. The prediction that Church and State would unite to persecute those who keep the commandments of God has been pronounced groundless and absurd. It has been confidently declared that this land could never become other than what it has been, the defender of religious freedom. But as the question of enforcing Sunday observance is widely agitated, the event so long doubted and disbelieved is seen to be approaching, and the third message produces an effect which it could not have had before. {4SP 423.1}

Many reformers, in entering upon their work, determined to exercise great prudence...They hoped, by the example of a pure Christian life, to lead the people back to the doctrines of the Bible. But the Spirit of God came upon them as it came upon Elijah, and they could not refrain from preaching the plain utterances of the Bible,--doctrines which they had been reluctant to present. They were impelled to zealously declare the truth, and the danger which threatened souls. The words which the Lord gave them they uttered, fearless of consequences, and the people were compelled to hear the warning. {4SP 423.2}

Men of faith and prayer will be constrained to go forth with holy zeal, declaring the words which God gives them. The sins of Babylon will be laid open. The fearful results of a union of Church and State, the inroads of Spiritualism, the stealthy but rapid progress of the papal power,--all will be unmasked. By these solemn warnings the people will be stirred. Thousands upon thousands have never listened to words like these. In amazement they hear the testimony that Babylon is the church, fallen because of her errors and sins, because of her rejection of the truth sent to her from Heaven.

Exactly. And only these true chosen and faithful ones will be Christians. The Sunday keepers may call themselves Christian, but, they are far from it in reality.

The majority of "Christians" will be keeping Sunday. That will be the rest day enforced by the church/state.
But those who are among the "called, chosen and faithful" following the Lamb, will keep all God's moral law, including the Sabbath.