25 With the merciful you will show yourself merciful; with an upright man you will show yourself upright;
26 With the pure you will show yourself pure; and with the fraudulent you will show yourself devious.
Now for the psalmist, this was a matter of straight reward and retribution. In this Psalm, the Lord simply rewards us according to our righteousness (vs 20, 24), and punishes them according to their wickedness. But of course, this becomes problematic for the psalmist, the prophets and especially Job when the recompense appears to be arbitrary, disproportionate or unjustly reversed. Jeremiah, scratching his head and wiping his tears prays,
You are always righteous, LORD, when I bring a case before you. Yet I would speak with you about your justice: Why does the way of the wicked prosper? Why do all the faithless live at ease? (Jer. 12:1 NIV)