Seal on the foreheads of the servants of out God

Revelation 7:1-8
A pause in tribulation, 144000 Jews will turn to the Lord.
Four angels standing at the four corner so the earth, holding back the four winds of the earth to prevent any wind from blowing on the land or on the sea or on any tree. They have power to harm the land and the sea. -- Hot weather, tornado.
Another angel coming up from the east, having the seal of the living God.
"Do not harm the land or the sea or the trees until we put a seal on the foreheads of the servants of out God." loud voice called out.
The four winds may be the same as the four horsemen of chapter 6. If so John sees the forces of destruction held back while God sets his mark of ownership on everyone who belongs to him.
After this: indicates a new vision, not later in time than the events of chapter 6.
144000: A symbolic number: the total of all God's people(12x12x1000), identical with the 'great multiple'(v9). See numbers with special meaning. We take Israel to mean, not the nation, but God's people - Old Testament believers and new Testament Christians alike.
Dan is omitted from this list. Unusually, both Joseph and his son Manasseh are included (but not Joseph's other son Ephraim); Manasseh was the firstborn.
Why?
Those who live along the seacoast or in an area subject to tornadoes can understand this text better than those who yearn for refreshing breezes in the desert. 
In each case John's vision accomplishes a transformation (compare Gundry 1987:260). A Lion is transformed into a Lamb, and 144,000 Jews are transformed into an innumerable multitude from every nation on earth!
Some scholars believe the tribe of Dan is missing because the Jewish Antichrist, known as the False Prophet, will be a descendant. This certainly seems to be the meaning of an ancient prophecy that Jacob gave about the tribes of Israel in the last days: "Dan will be a serpent in the way, a venomous viper by the path, that bites the horse's heels so that his rider falls backward".(Gen. 49 v.17) We can expect the Holy Spirit to move on the hearts of people at the beginning of the Tribulation and culminate with the second coming of Christ.
How?
Selected one who may escape from the disaster of that day!