God wants us to be the best that we can be - and to do the best that we can do - but doesn't expect us to go beyond that. God created us as human beings and wants us to engage with us as human, and God is able to cope with our flaws.
I have just started reading Thomas Merton's The Ascent to Truth. Merton recognises the need for us to remain within the limits that our humanity imposes when he writes: "The Church does not seek to sanctify men (sic) by destroying their humanity, but by elevating it, with all its faculties and gifts."
Of course, it is also true that we need God's help if we are going to be the best that we can be.