16 Let us inquire then what he has called tradings, which indeed he that has not known, all the day long does praise God. Trading even in the Greek language is derived from action, and in the Latin from want of inaction: but whether it be from action or want of inaction, let us examine what it is. For they that are active traders, rely as it were upon their own action, they praise their works, they attain not to the grace of God. Therefore traders are opposed to that grace which this Psalm does commend. For it does commend that grace, in order that no one may boast of his own works. Because in a certain place is said, “Physicians shall not raise to life,” ought men to abandon medicine? But what is this? Under this name are understood proud men, promising salvation to men, whereas “of the Lord is Salvation.”...With reason the Lord drove from the Temple them to whom He said, “It is written, My House shall be called the House of prayer, but you have made it a house of trading;” that is, boasting of your works, seeking no inaction, nor hearing the Scripture speaking against your unrest and trading, “be ye still, and see that I am the Lord.”...
Source: The Enarrations, or Expositions, on the Psalms (New Advent)