We often forget the context for this passage. Jesus is answering his disciples' question about how it could be possible to carry on with your life if you do what Jesus has just said and sell all your possessions and give the proceeds to the poor. It's a legit question. Jesus, as is his won't, responds with the esoteric aphorism quoted above "For mortals it is impossible; but for God all things are possible."
Understably, Peter is not satisfied with this non-answer; so, he says, "Look, we have left everything and followed you. What then will we have?" Jesus responds that they will receive abundant recompense, I.e the "manifold" and "eternal life." However, it is not clear what this "manifold" is or if it is to be received in the here and now or when. It doesnt help that Jesus closes the chapter with "But many who are first will be last, and the last will be first." (Thanks for the clarification!)
The issue with reading this passage as an assurance that God will repay the sacrifice with worldly glory and riches is that Jesus's whole point is that these things should be abandoned. Why would Jesus reward a rejection of worldly achievement with worldly achievement?
I think a better reading of "through God, all things are possible" is faith and keeping the law will show you the righteousness of giving everything away . . . even though you can't actually do it.