Originally it was the angel of death passing over the houses marked with the blood of lamb without defects placed over the door. As the angels of death are coming again (Mt 13:39-40) (Rev 8:7), how will they determine what houses to bypass (Dt 6:8-9)? Those with the mark of the beast, apparently will have something to worry about.(Rev 19:20-21) The mark of God seems pretty evident (Dt 6:8). What is the mark of the beast, and who is the beast, and who are his two horns, and what is their relevance?
If you want to be "passed over".... repent of sin, be baptized for remission of sins (transgression of GOD'S law) and receive the gift of God's spirit (a spirit of power, love and a sound mind) within you (it is first with you, then in you) at the laying on of hand's of God's ministers. They will be keeping and teaching the commandments and holy days GIVEN BY GOD -and preaching the gospel OF THE KINGDOM before the end.
The sign between God and his people -as frontlets between the eyes (forehead) and as a sign on the hand -are the commandments and holy days given by God -as well as statutes and judgments under the law which now apply. The mark of the beast is GENERALLY submission to (forehead) -and practice of (hand) -anything contrary -though some things also specifically.
All of this is essentially the way to have the blood of the lamb's sacrifice (Christ) 'applied'.
Not all who keep God's commandments will escape what is to come -some will go into the tribulation and be saved out of it ( either to be purified and/or to serve God in it) along with a great multitude of all nations, but it is certainly a good idea to do the following -as some will literally be led to a place of safety by God during the worst time of trouble the world has ever known -or will ever know.....
Luke 21:35For as a snare shall it come on all them that dwell on the face of the whole earth.
36Watch ye therefore, and pray always, that ye may be accounted worthy to escape all these things that shall come to pass, and to stand before the Son of man.
Rev 12:6And
the woman fled into the wilderness, where she hath a place prepared of God, that they should feed her there a thousand two hundred and threescore days.
(the different churches in Revelation were originally in different places, but also represent eras of God's church over time -the second to last described here... the last group being separated from them by one being protected and one going onto the tribulation)
Rev3:7And to the angel of the church in Philadelphia write; These things saith he that is holy, he that is true, he that hath the key of David, he that openeth, and no man shutteth; and shutteth, and no man openeth;
8I know thy works: behold, I have set before thee an open door, and no man can shut it: for thou hast a little strength, and hast kept my word, and hast not denied my name.
9Behold, I will make them of the synagogue of Satan, which say they are Jews, and are not, but do lie; behold, I will make them to come and worship before thy feet, and to know that I have loved thee.
10Because thou hast kept the word of my patience, I also will keep thee from the hour of temptation, which shall come upon all the world, to try them that dwell upon the earth.