What must I do to inherit eternal life? It is a question we hear repeated in Acts 2 when the crowd asks Peter "What must we do...?" But Jesus catches what Peter misses, the first person pronoun.
With humans it is not possible. I, me, we, us - can not DO anything to inherit eternal life. Even if we kept all the commandments. Even if we lived by all the 618ish dietary, cleanliness, ritual laws of Moses. Even if we lived up to the Great Commandments. There would still be something else because as soon as we think we've got it under control, we've failed, pride has entered, and another payment would be due.
"Who than can be saved?" Finally, the disciples ask a wise question. The intention behind it is no doubt selfish, but at lest the question is good. Everyone can be saved because everyone is in need of saving. Everyone can be saved so long as they cry out to thou for help. Everyone can be saved because it isn't up to me/us to DO anything, it is only up to God's graciousness - which is all encompassing.
This passage from Mark's Gospel is all about perspective; all about I vs. thou. May we remember this day from whom our help is to come.