According to the Catechism of the Catholic Church, "Justice is the moral virtue that consists in the constant and firm will to give their due to God and neighbor. Justice toward God is called the 'virtue of religion.' Justice toward men disposes one to respect the rights of each and to establish in human relationships the harmony that promotes equity with regard to persons and to the common good" (#1807). Justice prompts us to pay debts owed to others, to keep promises and commitments, to obey just laws made by those who have authority to make them, to play games fairly, and to respect the property of others. Justice directs us to act fairly and honestly toward others.
There are some debts we can never repay; for example, the debt we owe to God who created us, to our parents for giving us life and raising us, or to our country. The respect, love, and loyalty that we show to them are derived from the virtue of justice.