How do we know the doctrine of heavenly rewards is true?

The doctrine of heavenly rewards is rooted in Jesus' teaching found in passages like Mark 10:28-31 and Matthew 20:27-16. Here, Jesus assures His followers that sacrifices made for Him and the gospel will be rewarded not just in eternity, but in this life as well, emphasizing the abundant grace God extends to those who follow Him. Furthermore, Jesus compares the kingdom of heaven to various parables, like the workers in the vineyard, illustrating that God's generosity is not contingent on our works but rooted in His grace. The idea that works correlate to rewards is an expression of divine grace. However, it's crucial to understand that these rewards should not be perceived in a mercenary manner; they are given freely by God's grace, which can’t be earned.