In this verse we hear something of the Messianic kingship that David adhered to. David's kingship was supposed to show the kingship of God on earth. It was a shadow of the reign of the Messiah (the Prince of Peace); so there was no place for people who by their words or deeds tried to kill other people. Just put Psalm 101:1–8 beside this. It does create somewhat of an ideal situation; with David too, the Messianic aspect was sometimes hard to find. But in line with the heart of the heavenly King, it had to be this way: no place for slanderers; loyalty and justice are of paramount importance. This is something for us to consider when we think about life in the church as well.
12 L'homme dont la langue est fausse ne s'affermit pas sur la terre;Et l'homme violent, le malheur l'entraîne à sa perte.