1 What does this recollection of the Sabbath mean? What is this Sabbath? For it is with groaning that he “calls it to recollection.” You have both heard already when the Psalm was read, and you will now hear it when we shall go over it, how great is his groaning, his mourning, his tears, his misery. But happy he who is wretched after this manner! Whence the Lord also in the Gospel called some who mourn blessed. “How should he be blessed if he is a mourner? How blessed, if he is miserable?” Nay rather, he would be miserable, if he were not a mourner. Such an one then let us understand here too, calling the Sabbath to remembrance (viz.), some mourner or other: and would that we were ourselves that “some one or other”! For there is here some person sorrowing, groaning, mourning, calling the Sabbath to remembrance. The Sabbath is rest. Doubtless he was in some disquietude, who with groaning was calling the Sabbath to remembrance....
2. “O Lord, rebuke me not in Your indignation; neither chasten me in Your hot displeasure”. For it will be that some shall be chastened in God's “hot displeasure,” and rebuked in His “indignation.” And haply not all who are “rebuked” will be “chastened;” yet are there some that are to be saved in the chastening. So it is to be indeed, because it is called “chastening,” but yet it shall be “so as by fire.” But there are to be some who will be “rebuked,” and will not be “corrected.” For he will at all events “rebuke” those to whom He will say, “I was an hungred, and you gave me no meat.”... “Neither chasten me in Your hot displeasure;” so that You may cleanse me in this life, and make me such, that I may after that stand in no need of the cleansing fire, for those “who are to be saved, yet so as by fire.” Why? Why, but because they “build upon the foundation, wood, stubble, and hay.” Now they should build on it, “gold, silver, and precious stones;” and should have nothing to fear from either fire: not only that which is to consume the ungodly for ever, but also that which is to purge those who are to escape through the fire. For it is said, “he himself shall be saved, yet so as by fire.” And because it is said, “he shall be saved,” that fire is thought lightly of. For all that, though we should be “saved by fire,” yet will that fire be more grievous than anything that man can suffer in this life whatsoever....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)