This is an obvious sign of the righteous judgment of God, to the end that you may be counted worthy of the Kingdom of God, for which you also suffer.
The phrase "be counted worthy" (kataxio-omai) means "to account worthy, judge worthy" (Thayer 335-1-2661). The "kingdom of God" refers to heaven. Heaven is a prepared place for a prepared people (John 14:1-3). We need to devote our all in defending the cause for which our Lord died and promote His cause to every nation and to every creature (Matthew 28:18-20; Mark 16:15-16). Our labors will not be vain (1 Corinthians 15:58), and we will receive a crown of life if we are faithful unto death (Revelation 2:10).