Today's verse of Psalm 140 is another that is hard to understand by just looking at the words; we have to do some work to get at the true meaning.
Looking at the Latin
| 
   8  | 
  
   V  | 
  
   Audient verba mea quoniam potuerunt: * sicut
  crassitudo terræ erupta est super terram.  | 
 
| 
   OR  | 
  
   audient verba mea quoniam
  potuerunt sicut crassitudo terrae eructuat super terram  | 
 |
| 
   NV  | 
  
   audient verba
  mea, quoniam suavia erant. Sicut frusta dolantis et dirumpentis in terra,   | 
 |
| 
   
  | 
  
   JH  | 
  
   et audient uerba mea, quoniam decora
  sunt. Sicut agricola cum scindit terram,   | 
 
| 
   
  | 
  
   Sept  | 
  
   ἀκούσονται τὰ ῥήματά μου ὅτι ἡδύνθησαν ὡσεὶ
  πάχος γῆς διερράγη ἐπὶ τῆς γῆς   | 
 
Phrase by phrase
| 
   Audient verba
  mea  quoniam
  potuerunt:  sicut
  crassitudo terræ  erupta est
  super terram.  | 
  
   They shall hear my
  words, for they have
  prevailed:  As when the
  thickness of the earth  is broken up upon
  the ground  | 
 
Audient (they shall hear) verba (words) mea (my) quoniam (as/because) potuerunt (they are powerful/they shall prevail): sicut (just as) crassitudo (a clod) terræ (of earth) erupta est (is broken up) super (on) terram (the ground).
Key vocabulary
possum, potui, posse (1) to be able, to have power (2) to prevail,
attain
crassitudo – inis f thickness, a clod
erumpo ere rupi ruptum (3) to break
up, crush 
It should be noted that St John Chrysostom supplies several different text variants for the second phrase, which Robert Hill translates variously as:
- As thickness of earth is smashed on the ground, our bones were scattered near Hades;
 - Like a farmer harrowing the soil, so our bones were scattered in the mouth of Hades;
 - Like someone breaking up and cleaving the soil, our bones were cast into Hades; and
 - Like someone improving and digging up the soil, our bones were scattered near Hades.
 
Selected English translations
| 
   DR  | 
  
   They shall hear my
  words, for they have prevailed: As when the thickness of the earth is broken
  up upon the ground:   | 
 
| 
   Brenton  | 
  
   they shall hear my words, for they are
  sweet. As a lump of earth is crushed upon the ground  | 
 
| 
   MD  | 
  
   They shall hear that my words have
  prevailed: as clods of earth thrown upon the ground.  | 
 
| 
   RSV  | 
  
   then they shall learn that the word of the
  LORD is true. As a rock which one cleaves and shatters on the land,  | 
 
| 
   Cover  | 
  
   that they may
  hear my words, for they are sweet.   | 
 
| 
   Knox  | 
  
   a people whose bones lie scattered at the
  grave’s mouth, like seed when the earth is cloven into furrows  | 
 
| 
   Grail  | 
  
   then they understood that my words were
  kind. As a millstone is shattered to pieces on the ground  | 
 
[Key: DR=Douay-Rheims Challoner; MD=Monastic Diurnal; RSV=Revised Standard Version; Cover=Coverdale]
The truth will prevail
The first half of the verse can be read as a statement that ultimately, many who reject Christ, or twist his meanings into heresy will eventually be converted. St Jerome puts it thus:
The Lord himself says: They who came to me were won over, and they delighted in my words and were converted to me in my Church.
Similarly, St Augustine argues it means that the truth will win out in the end, over the clever lies and conceits of those who work evil:
My Words have prevailed over their words. They have spoken clever things, I true things. To praise one who talks well is one thing, to praise One who speaks truth is another.
Ploughing stone hearts
The key question is, though, what brings about this change of heart?
There are several different interpretations of this part of the verse, depending on whether you see it as connected to what came before, or what comes next.
St Robert Bellarmine's explanation is the most simple and compelling I think, seeing it as an analogy to the farmer plowing hard soil in order to make it ready to be planted:
An allusion to “My prayer also shall still be against the things with which they are well pleased;” by which he gives us to understand that many unfortunate souls, who prided themselves on their sins, would hear his words, and be converted to God through them; for as the hardest soil is entered by the plough, so the heart of man, however hardened it may be, will be entered and stirred up by the power and the efficacy of the word of God. Those poor souls, already alluded to, will hear my words; for these words were most effectual in moving them; as effectual as a spade or a plough, to enter into and turn up the thick, sluggish clay.
St Augustine ties the verse to what follows, seeing the reference in the next verse to 'our bones' lying on ground as carrying forward the farming analogy to the martyrs as fertiliser for the Church:
Behold, I send you forth as sheep in the midst of wolves. Fear not those who kill the body, etc. He gave them fear, He suggested hope, He kindled love. Fear not death, He says. Do ye fear death? I die first. Fear ye, lest a hair of your head perish? I first rise again in the flesh uninjured. Rightly have ye heard His Words, for they have prevailed. They spoke, and were slain; they fell, and yet stood.
And what was the result of so many deaths of martyrs, save that those words prevailed, and the earth being, so to speak, watered by the blood of Christ's witnesses, the cross of the Church shot up everywhere? How have they prevailed? We have said already, when they were preached by men who feared not. Feared not what? Neither banishment, nor losses, nor death, nor crucifixion: for it was not death alone that they did not fear; but even crucifixion, a death than which none was thought more accursed. It the Lord endured, that His disciples might not only not fear death, but not even that kind of death. When then these things are said by men that fear not, they have prevailed.
| 
   Vulgate  | 
  
   Douay-Rheims  | 
 
| 
   Psalmus
  David.  | 
  
   A psalm of David.  | 
 
| 
   1 Dómine, clamávi ad te, exáudi me: * inténde voci meæ,
  cum clamávero ad te.  | 
  
   I
  have cried to you, O Lord, hear me: hearken to my voice, when I cry to you.  | 
 
| 
   2  Dirigátur
  orátio mea sicut incénsum in conspéctu tuo: * elevátio mánuum meárum
  sacrifícium vespertínum.  | 
  
   2 Let my prayer be directed as incense in your
  sight; the lifting up of my hands, as evening sacrifice.  | 
 
| 
   3  Pone,
  Dómine, custódiam ori meo: * et óstium circumstántiæ lábiis meis.  | 
  
   Set a watch, O Lord, before my mouth: and a door
  round about my lips.   | 
 
| 
   4  Non
  declínes cor meum in verba malítiæ: * ad excusándas excusatiónes in peccátis.  | 
  
   4 Incline not my heart to evil
  words; to make excuses in sins.   | 
 
| 
   5  Cum homínibus operántibus iniquitátem: * et non
  communicábo cum eléctis eórum  | 
  
   With
  men that work iniquity: and I will not communicate with the choicest of them  | 
 
| 
   6  Corrípiet
  me justus in misericórdia, et increpábit me: * óleum autem peccatóris non impínguet
  caput meum.  | 
  
   5 The just man shall correct
  me in mercy, and shall reprove me: but let not the oil of the sinner fatten
  my head.   | 
 
| 
   7
   Quóniam adhuc et orátio mea in beneplácitis eórum: * absórpti sunt
  juncti petræ júdices eórum.  | 
  
   For my prayer shall still be against the things
  with which they are well pleased: 6 Their
  judges falling upon the rock have been swallowed up.   | 
 
| 
   8  Audient verba mea quóniam potuérunt: * sicut
  crassitúdo terræ erúpta est super terram.  | 
  
   They shall hear my words, for they have prevailed: 7 As when the thickness of the earth is broken up
  upon the ground:   | 
 
| 
   9 
  Dissipáta sunt ossa nostra secus inférnum: * quia ad te, Dómine, Dómine,
  óculi mei: in te sperávi, non áuferas ánimam meam.  | 
  
   Our bones are scattered by the side of hell. 8 But to you, O Lord, Lord, are my eyes: in you have
  I put my trust, take not away my soul.   | 
 
| 
   10  Custódi
  me a láqueo, quem statuérunt mihi: * et a scándalis operántium iniquitátem.  | 
  
   9 Keep me from the snare,
  which they have laid for me, and from the stumbling blocks of them that work iniquity.
    | 
 
| 
   11  Cadent
  in retiáculo ejus peccatóres: * singuláriter sum ego donec tránseam.  | 
  
   10 The wicked
  shall fall in his net: I am alone until I pass.  | 
 
For the next part in this series on Psalm 140, continue on here.