Some Sabbatarian Christians maintain that the Sabbath is the seal of God and that Sabbath-keeping will be for Christians a test of loyalty to God in the troublous times preceding Christ's Second Coming. But does Scripture support this assertion? Let's take a look at 2 Corinthians 1, and Ephesians 1 and 4.

The Holy Spirit of promise makes Christians firm in the faith of the Gospel, allowing the believer to live a life pleasing to God, and providing assurance of salvation.

God has made known to believers through Christ, the Spirit of truth, this promise of salvation. Through Christ, God and humanity formerly estranged, are now reconciled; and the penalty of sin is satisfied for the wrong which caused the separation. He brought about, by His Spirit, the benefits of faith and love, whereby we are united with God. The sanctifying and comforting influences of the Holy Spirit seal or designate believers as the children of God, and the beneficiaries of eternal life. All to the glory of God.

Ephesians 4:30
"And do not grieve the Holy Spirit of God, by whom you were sealed for the day of redemption."

Anything that arouses evil desires and lusts grieve the Spirit of God. Corrupt passions such as bitterness, rage, anger, a complaining attitude, slander, and malice sadden the Holy Spirit. The continuation of these things in one's life causes the Spirit of God to remove His presence and His sanctifying influences. When the believer has the Holy Spirit living within, that person can truly be kind, compassionate, forgiving, and bear good fruit (Galatians 5:22-23). Woe to one if the Spirit should depart due to willful rejection of His guidance, but salvation is assured to the person in whom the Spirit dwells.

The important point here, however, is that instead of the Sabbath being the seal of God, it appears that the Holy Spirit is. Those who accept Christ by faith receive the seal of God, which is the Holy Spirit. And this seal is received at the moment of acceptance, not at some future date or time. There is no real Scriptural support for the belief that Sabbath-keeping will be for Christians a test of loyalty to God just before Christ's Second Coming.