10 Moreover, seventy and eighty years equal a hundred and fifty; a number which the Psalms clearly insinuate to be a sacred one. One hundred and fifty have the same relative signification as fifteen, the latter number being composed of seven and eight together: the first of which points to the Old Testament through the observation of the Sabbath; the latter to the New, referring to the resurrection of our Lord. Hence the fifteen steps in the Temple. Hence in the Psalms, fifteen “songs of degrees.” Hence the waters of the deluge overtopped the highest mountains by fifteen cubits: and many other instances of the same nature. “Our years are passed in thought like a spider.” We were labouring in things corruptible, corruptible works were we weaving together: which, as the Prophet Isaiah says, by no means covered us. “The days of our years are in themselves,” etc. A distinction is here made between themselves and their strength: “in themselves,” that is, in the years or days themselves, may mean in temporal things, which are promised in the Old Testament, signified by the number seventy; “but if” not in themselves, but “in their strength,” refers not to temporal things, but to things eternal, “fourscore years,” as the New Testament contains the hope of a new life and resurrection for evermore: and what is added, that if they pass this latter period, “their strength is labour and sorrow,” intimates that such shall be the fate of him who goes beyond this faith, and seeks for more. It may also be understood thus: because although we are established in the New Testament, which the number eighty signifies, yet still our life is one of labour and sorrow, while “we groan within ourselves, awaiting the adoption, to wit, the redemption of our body; for we are saved by hope; and if we hope for that we see not, then do we with patience wait for it.” This relates to the mercy of God, of which he proceeds to say, “Since your mercy comes over us, and we shall be chastened:” for “the Lord chastens whom He loves, and scourges every son whom He receives,” and to some mighty ones He gives a thorn in the flesh, to buffet them, that they may not be exalted above measure through the abundance of the revelations, so that strength be made perfect in weakness. Some copies read, we shall be “taught,” instead of “chastened,” which is equally expressive of the Divine Mercy; for no man can be taught without labour and sorrow; since strength is made perfect in weakness.
11. “For who knows the power of Your wrath: and for the fear of You to number Your anger?”. It belongs to very few men, he says, to know the power of Your wrath; for when Thou dost spare, Your anger is so far heavier against most men; that we may know that labour and sorrow belong not to wrath, but rather to Your mercy, when You chasten and teachest those whom You love, to save them from the torments of eternal punishment: as it is said in another Psalm, “The sinner has provoked the Lord: He will not require it of him according to the greatness of His wrath.” With this also is understood, “Who knows?” Such is the difficulty of finding any one who knows how to number Your anger by Your fear, that he adds this, meaning that it is to the purpose that Thou appearest to spare some, with whom You are more angry, that the sinner may be prospered in his path, and receive a heavier doom at the last. For when the power of human wrath has killed the body, it has nothing more to do: but God has power both to punish here, and after the death of the body to send into Hell, and by the few who are thus taught, the vain and seductive prosperity of the wicked is judged to be greater wrath of God....
12. “Make Your right hand so well known”. This is the reading of most of the Greek copies: not of some in Latin, which is thus, “Make Your right hand well known to me.” What is, “Your right hand,” but Your Christ, of whom it is said, And to whom is the Arm of the Lord revealed? Make Him so well known, that Your faithful may learn in Him to ask and to hope for those things rather of You as rewards of their faith, which do not appear in the Old Testament, but are revealed in the New: that they may not imagine that the happiness derived from earthly and temporal blessings is to be highly esteemed, desired, or loved, and thus their feet slip, when they see it in men who honour You not: that their steps may not give way, while they know not how to number Your anger. Finally, in accordance with this prayer of the Man that is His, He has made His Christ so well known as to show by His sufferings that not these rewards which seem so highly prized in the Old Testament, where they are shadows of things to come, but things eternal, are to be desired. The right hand of God may also be understood in this sense, as that by which He will separate His saints from the wicked: because that hand becomes well known, when it scourges every son whom He receives, and suffers him not, in greater anger, to prosper in his sins, but in His mercy scourges him with the left, that He may place him purified on His right hand. The reading of most copies, “make Your right hand well known to me,” may be referred either to Christ, or to eternal happiness: for God has not a right hand in bodily shape, as He has not that anger which is aroused into violent passion.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)