How does St Peter's view on salvation reconcile with that of Jesus?

We read in Mt 21:31 : > Which of the two did the will of his father?” They said, “The first.” Jesus said to them, “Truly I tell you, the tax collectors and the prostitutes are going into the kingdom of God ahead of you. We also read in 1 Pet 4:18: > And “If it is hard for the righteous to be saved, what will become of the ungodly and the sinners?” While we see the generosity of Jesus in welcoming one and all to salvation, we see St Peter talking tough. It appears that St Peter is quoting someone, but his source is not clear to the reader. My question, therefore is: According to Catholic scholars, is St Peter quoting someone in 1 Pet 4:18 ? If not, how does his view on salvation reconcile with that of Jesus in Mt 21: 31 ?