10 But this man seeks what he may return unto the Lord, and finds not, save out of those things which the Lord Himself returns. “I will receive,” he says, “the cup of salvation, and call upon the Name of the Lord”. “My vows will I render to the Lord, before all His people”. Who has given you the cup of salvation, which when you take, and callest upon the Name of the Lord, you shall return unto Him a reward for all that He has returned unto you? Who, save He who says, “Are ye able to drink the cup that I shall drink of?” Who has given unto you to imitate His sufferings, save He who has suffered before for you? And therefore, “Right dear in the sight of the Lord is the death of His Saints”. He purchased it by His Blood, which He first shed for the salvation of slaves, that they might not hesitate to shed their blood for the Lord's Name; which, nevertheless, would be profitable for their own interests, not for those of the Lord.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)