Grace
Grace it is said is 'getting what you don't deserve'.
Have you ever felt overwhelmed by something someone did for you - you feel you didn't really deserve it but nevertheless you are really bowled over that they have done it for you? Grace is a generosity beyond whether someone else deserves to get what you are giving them. You don't have to give them this thing but you decide you want to because you care about them.
Well this describes what God has done for us in sending Jesus - his only son. He sent him to die in our place. He gave the life of his son away so that we could be saved, not because we deserved it or because we are particularly worthy of the gift, but because he knew we could not save ourselves.
It is also on-going. In all our dealings Jesus challenges us to a way of grace. He knows what it's like to live life. He knows people will let you down, even hurt you. But the way of grace is a way of giving forgiveness even when it's not deserved - giving up your time, effort and possessions to make sure others don't go without. It is love in action - not just love for those you love naturally, but often for those you would not usually even consider.
Eph 2:8
'It is by grace you have been saved, through faith - and this not from yourselves, it is the gift of God - not by works, so that no one can boast.'