Everyone is a Saint in Heaven, nobody in Heaven is not a Saint.
If I can use a metaphor, my understanding is that your reward in Heaven is an endless flow of God’s Grace. The things you do in life here on earth either “grow” or “shrink” your cup of grace. So if you were more open to God in this life, your cup will grow and you will receive more. If otherwise you will still fill your cup, God will completely fill up everyone cups, its just some will have more and some less. Everyone will be completely satisfied because they will receive an overflowing cup no matter what, God’s graces are endless.
Another thing that used to bother me but doesn’t anymore now that I have accepted it, is this: God makes you exactly how you were suppose to be made. Because of this there are some people who will be inherently “open to more graces” than you are. That’s just how it is. People that come to mind are: Mary the Mother of God, Padre Pio, Mother Teresa, you get the point…I used to be frustrated in thinking “I want to get the most out of Heaven, how come I just can’t be as Holy as other people.” The beauty of it is, is that God made you specifically how you are suppose to be made. You are a completely unique “tool” that has a completely unique purpose in life.
The point is, when Jesus talks about the greatest among us being the least among us we have to realize that the only thing you can choose do to in this life is be either open to what God wants you to do or not. Don’t worry about the rewards in Heaven because the second you start thinking about them the second your focus is pointed inward instead of toward your neighbor…sounds a lot like a particularly evil fallen angel I know…
…and I’m not saying: “don’t think about Heaven its bad!” Its just that God already knows where people are going to go, what people are going to receive in Heaven. The only thing you can do is trust that God has it covered and keep following and doing his will.