Martin Luther, commenting on Galatians 5:14, wrote:
Therefore the apostle admonishes Christians seriously, after they have heard and accepted the pure doctrine about faith, to practice genuine works as well. For in the justified there remain remnants of sin, which deter and dissuade them both from faith and from truly good works. In addition, the human reason and flesh, which resists the Spirit in the saints (in the wicked, of course, it has dominant control), is naturally afflicted with Pharisaic superstitions and, as Ps. 4:2 says, “loves vain words and seeks after lies”; that is, it would prefer to measure God by its own theories rather than by His Word and is far more ardent about doing works that it itself has chosen than about doing those that God commands.
Luther, Martin Luther’s Works, volume 27: Lectures on Galatians 54