What does Jesus mean by 'the last shall be first'?

'The last shall be first' is a principle that highlights the radical nature of God's grace and the inversion of expectations regarding salvation. In the narrative of the rich young ruler, the disciples were astonished by Jesus' teaching about wealth and its obstacle to entering the kingdom of God. By stating this principle, Jesus illustrates that those who appear outwardly righteous may not find favor in God's eyes merely based on their status. Instead, it is those who come humbly and recognize their need for grace who will be exalted. This underscores the Reformed understanding that salvation is not based on human effort or achievements but on God's sovereign choice and grace.