10 Wherefore, consistently with this, he adds the last words, and says, “Since You, O Lord, in singleness hast made me dwell in hope.” Here he does not say, wilt make; but, “hast made.” In whom then this hope now is, there will be assuredly that which is hoped for. And well does he say, “in singleness.” For this may refer in opposition to those many, who being multiplied from the time of His grain, of wine, and oil, say, “Who shows us good things?” For this multiplicity perishes, and singleness is observed among the saints: of whom it is said in the Acts of the Apostles, “and of the multitude of them that believed, there was one soul, and one heart.” In singleness, then, and simplicity, removed, that is, from the multitude and crowd of things, that are born and die, we ought to be lovers of eternity, and unity, if we desire to cleave to the one God and our Lord.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)