Revelation 7:4 And I heard the number of those who were sealed. One hundred and forty-four thousand of all the tribes of the children of Israel were sealed:

Once again this verse shows the importance of Israel in the end times.
God seals 144,000 and reveals that 12,000 come from 12 tribes of Israel.
In the list, Levi and Joseph are added and Ephraim and Dan are missing. However, Ephraim is a son of Joseph and so perhaps Ephraim is meant by being a descendant.
In his blessing of his sons, Jacob (Israel) said, “Dan shall be a serpent by the way, a viper by the path, that bites the horse’s heels so that its rider shall fall backward.” Gen 49:17
Some scholars speculate that someone from Dan is involved with the world leader of Revelation, perhaps even the false prophet is from Dan.
I know this, 144,000 Hebrews are sealed. Not Gentiles!
The book is a revelation of the Messiah to the seed of Abraham.
These are sealed by God and ready to serve.
Can you imagine something like 144,000 Elijah’s or Jeremiah’s let loose on the world?
Now some erroneously believe the 144,000 represent the total of redeemed souls. It is not so. John will see a multitude before God that no man can number.
In conclusion, I do not say you cannot be saved during the tribulation period of Revelation. I do believe it is difficult because of the great deception that is going on.
My advice to you is not wait.
Accept Jesus as Savior today.
Do not play church!
Do not depend on your goodness.
Do not depend upon your church membership.
Depend on Jesus.