Revelation 7:1-8
John is given another vision after these things, meaning after the first six seals that are revealed to him. He now sees four angels standing on the four corners of the earth holding the four winds of the earth in order that the wind should not blow on the earth, nor on the sea, nor on any tree until Gods servants were sealed.
These servants are the generational 144,000 from the twelve tribes of Israel, except for the tribe of Dan and Ephraim as they fell to idol worship and allowed God to be removed from them, Judges 18:30; 1 Kings12:25-33; Hosea 5:9, 11;Psalms 78:9-17, 65-67. To keep it twelve tribes since Dan and Ephraim are not mentioned in vs. 4-8 the tribe of Joseph appears twice, once under his own name and once under the name of his son Issachar/Manasseh. Judah is mentioned first as Messiah was to come from the lineage of David.
This is the importance of the 144,000 of the house of Israel and their generations unto the end of days. There were those of the old covenant that were faithful to God in keeping all his commandments and repented of their idol worshipping. Their generations who have also come back to Gods grace that are still alive during the seven trumpet sounds will continue to preach to the Jews as it was with the twelve disciples in Matthew 10:6. The generations of the 144,000 that are still alive have the seal of God on them which are the seven Spirits of God as they will have to endure much persecution until the end of days before the return of Jesus.
(Seven Spirits of God are found in Isaiah 11:2 and mentioned in Rev 1:4. Spirit of the Lord, wisdom, understanding, counsel, power, knowledge and fear/respect of the Lord.)
