Growing up I had always been taught that Mt 1:19 was an apt illustration of the love vs. justice problem that pervades much of evangelical ethical thinking. For many evangelicals this passage provides an example of the inevitable teleological vs. deontological tensions we face in life. Good evangelicals are to take their cue from Joseph, feeling the teleological urge but ultimately being bound to doing “the right thing,” trying to follow the universally valid principles of justice no matter what.
However, why should verse 20, where the angel of the Lord tells Joseph to not follow through on this decision, be read in this dualistic fashion? Isn’t it entirely possible that Joseph, operating from his limited vantage point, was basing his decision not on the command of God but on abstract ethical maxims? It is only when the Lord breaks through this abstraction via his angel that Joseph learns what he is supposed to do. In this more Barthian reading of the passage Joseph is not some tragic western ethical hero, always willing to do right no matter what. Instead, he is sinning by attempting be righteous without knowing the concrete will of God, relying merely on a merely abstract principle of righteousness. Once he had “resolved” to follow through on this decision without seeking the will of God, only God could break through to show him his error.
Divorcing the greatest commandment from how one conceives of just living no doubt can lead us down tyrannical paths, some with implications so severe that God must send his angels to break through to us. More importantly, whenever we divorce our decision-making from seeking the concrete demand of God, reducing discipleship to an ethical calculus, we cannot help but go astray.