Mark 10:40

10:40 but to sit at my right or at my left is not mine to give. It is for those for whom it has been prepared.” ¹ 

Mark 8:38

8:38 For if anyone is ashamed of me and my words in this adulterous and sinful generation, the Son of Man will also be ashamed of him ²  when he comes in the glory of his Father with the holy angels.”

[10:40]  ¹ sn After the first passion prediction in 8:31 Jesus rebuked Peter as having been used by Satan. After the second passion prediction in 9:31 the disciples were concerned about who would be the greatest in the kingdom. After the third passion prediction in 10:33 James and John asked for positions of honor and rulership in the kingdom, revealing their complete misunderstanding of the nature of the kingdom and exposing their inadequacy as true disciples of Jesus. Jesus replied that such positions were for those for whom it has been prepared.

[8:38]  ² sn How one responds now to Jesus and his teaching is a reflection of how Jesus, as the Son of Man who judges, will respond then in the final judgment.