4 “The innocent of hand, and the pure in heart”. Who then shall ascend there, and abide there, but the guiltless in deed, and pure in thought? “Who has not received his soul in vain.” Who has not reckoned his soul among things that pass away, but feeling it to be immortal, has longed for an eternity steadfast and unchangeable. “And has not sworn in deceit to his neighbour.” And therefore without deceit, as things eternal are simple and undeceiving, has so behaved himself to his neighbour.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)