The Last Psalms of Vespers - Psalm 128

St Benedict's decision to make Psalm 128 the last psalm of Monday Vespers took some considerable contrivance.  

The placement of Psalm 128 on Monday

In order to achieve it, he makes Monday Vespers one of the longest of the week, by dint of not dividing one of the longest psalms used at the hour, and one that falls naturally into two parts (indeed it is listed as two separate psalms in the Maseoretic Text), Psalm 113; and has two combine two others, Psalm 115 and 116 under one doxology.

And on the face of it, it is a particularly odd decision, since it takes it out of the sequence of the rest of the Gradual Psalms that starts at Tuesday Terce and continues through Tuesday Vespers. 

There are, I think, several reasons for this.  The first is to do with his humility theme in the Office: the seven blocks of  Psalm 118 said over the day hours correspond, I think, to the first seven steps of humility set out in Chapter 7 of St Benedict's Rule, and this hour as a whole has links to to the eighth step, of following the common rule of the monastery.

Through those stripes and his cross, Christ has confounded the devil

Psalm 128 is one of the more difficult psalms to interpret just by reading the words literally. 

A simple Christological interpretation of it is that the devil has been confounded and repelled: all his efforts thwarted by the stripes Christ bore on his back (verse 3) for us, and the psalm appears in the Propers for Passion Sunday and elsewhere during Lent in exactly in that context.

Psalm 128 (129) – Saepe expugnaverunt me

Vulgate	Douay-Rheims
Canticum graduum.	A gradual canticle.
1 Sæpe expugnavérunt me a juventúte mea, * dicat nunc Israël:	Often have they fought against me from my youth, let Israel now say.
2  Sæpe expugnavérunt me a juventúte mea: * étenim non potuérunt mihi.	2 Often have they fought against me from my youth: but they could not prevail over me.
3  Supra dorsum meum fabricavérunt peccatóres: * prolongavérunt iniquitátem suam.	3 The wicked have wrought upon my back: they have lengthened their iniquity.
4  Dóminus justus concídit cervíces peccatórum: * confundántur et convertántur retrórsum omnes, qui odérunt Sion.	4 The Lord who is just will cut the necks of sinners: 5 Let them all be confounded and turned back that hate Sion.
5  Fiant sicut fœnum tectórum: * quod priúsquam evellátur exáruit:	6 Let them be as grass upon the tops of houses: which withers before it be plucked up:
6  De quo non implévit manum suam qui metit: * et sinum suum qui manípulos cólligit.	7 Who with the mower fills not his hand: nor he that gathers sheaves his bosom.
7  Et non dixérunt qui præteríbant: Benedíctio Dómini super vos: * benedíximus vobis in nómine Dómini.	8 And they that passed by have not said: The blessing of the Lord be upon you: we have blessed you in the name of the Lord.

St Jerome, however, also frames it as a description of the struggle we must all engage in against the devil and our own ill desires: this is the story of 'Christ's athlete' who:

 is not crowned unless he has accepted and sustained the challenge, unless his face is black and blue from the fray and bathed in blood.  discoloured bruises deserve a crown; suffering and pain merit joy. (Homily 45 on Psalm 128)

St Jerome goes further, though, goes on to argue that the claim that they could not prevail over me in verse 2 pertains particularly to the monk or nun who has served God from his early life onwards, and possesses integrity of body and spirit.

Uphold us Lord

Building on this, there is also a verbal link between verse 5's 'Let them all be confounded and turned back that hate Sion', and the verse of Psalm 118 used in the Benedictine profession ceremony:

Uphold me according to thy word, and I shall live: and let me not be confounded in my expectation. Suscipe me secundum eloquium tuum, et vivam, et non confundas me ab exspectatione mea.

Patristic exegesis of Scripture often fastened on the uses of a word in other verses of Scripture, creating chains of connections in meaning, thus Psalm 128 reflects that same prayer for God's protection against those who strive against us, and perhaps also warns against the consequences of we ourselves falling.

Let us all then, keep the model of Christ always in front of us, and beg for the grace that will ensure that our enemies not prevail over us.