Grace

Grace is someone (God Himself) and not something (as when we speak of 'different graces').  We often forget the nature of grace as a free gift, and consider our relationship with God to be something depending more on us than on Him (as when we speak of our 'preserving' or 'losing' grace).  In reality, we can lose everything, except grace, because grace is the gratuitous (not based on merit or as a reward) and unconditional love with which God gives himself to us.