- To be reckoned as righteous
- To demonstrate righteousness
The second has to do with someone's actions. It has to do with walking the walk. It is a demonstration of something within.
In the bible, the first is about God and man, and the second is mostly about man and man.
In the first case, God justifies man, declaring him to be righteous. Nothing changes about the man--God has simply agreed to treat the man as if he were righteous. The man receives a status update. God justifies the wicked (Rom. 4:5.) They are still wicked.
In the second case a man acts in what is perceived as a righteous manner, and justifies his righteousness (he may be a fraud) to his fellow man. He does not justify anything to God--God knows whether the man is righteous or not.
Abraham is the best example of the distinction between these two definitions. Abraham "crosses paths" with justification at two different times of his life and different passages in scripture. In Genesis 15, Abraham believes in God's promise of a multitude of descendants and his is justified in the first sense: God reckons him as righteous (Gen 15:6). Paul refers to this in Romans chapter 4. Years later, Abraham offers up his son Isaac. Of this event, James writes: Was not Abraham our father justified by works when he offered up Isaac his son on the altar? (James 2:21).
In the first event, God justified Abraham. In the second Abraham was justified in our eyes--not in God's. God had already justified Abraham. But Abraham demonstrates righteous behavior to us. We recognize him by his fruit. This form of justification is fallible--but it is what it is.