Why are the 144,000 a compensation for Israel?
Israel was originally intended to be the vehicle to bring the pagan Gentile world to a knowledge of Jehovah, but the nation missed that calling. The 144,000 compensate for that failure by fulfilling the role Israel forfeited, becoming believers who will enter the Kingdom.
Les explains that the 144,000 are a sort of compensation or evening out of what the nation of Israel utterly missed. Israel was originally intended to be the vehicles to bring the pagan, Gentile world to a knowledge of their Jehovah, but they missed it. The 144,000 will make a compensation for that. The surrounding context also notes that many from every tribe and tongue and nation will believe, be martyred almost as soon as they believe, though a few survive as believers and become candidates to enter the Kingdom when it is finally set up.