Is it still possible to buy ones way into paradise, as was practised in earlier times?
Answer: This immediately calls to mind the request of the two sons of Zebedee (Mk 10:35-40).
“James and John, the sons of Zebedee, came forward to him and said to him, Teacher, we want you to do for us whatever we ask of you. And he said to them, What is it you want me to do for you? And they said to him, Grant us to sit, one at your right hand and one at your left, in your glory. But Jesus said to them, You do not know what you are asking. Are you able to drink the cup that I drink, or be baptised with the baptism that I am baptised with? They replied, We are able. Then Jesus said to them, The cup that I drink you will drink; and with the baptism with which I am baptised, you will be baptised; but to sit at my right hand or at my left is not mine to grant, but it is for those for whom it has been prepared.”
In your kingdom, literally in your glory, means: When you triumph as the messianic King. Baptism is here the image of Jesus imminent passion. Jesus will be quasi immersed in an abyss of suffering. Is not mine to grant: Jesus mission on earth is not to distribute rewards to people but to suffer in order to save them, cf. Jn 3:17 and 12:47.
The Christian earns salvation by being as faithful as possible in imitating Christ and in trying to follow the path of selfless love, with the help and grace of Jesus, which he himself gave by his example.