For Christians the Old Testament becomes an entirely different book because we are required (and enabled) to read it through a new lens. This is seen immediately in the first Psalm. At first glance it is a poem about the great chasm that exists between "the wicked," and "the righteous." The original readers would interpret it as a warning to make sure we are on the right side of the line, squarely amongst the "right" folks who are doing the "right" stuff.
But to Christians it should remind us of our true predicament. We should be aware that "all have sinned and fallen short..." and remind us that our only hope for being declared righteous is through the grace of God and what he does for us in Christ. To a Christian Ps.1 becomes a song of gratitude for being declared righteous by faith and not by our own doing.
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