6 “They have bended the bow, a bitter thing, in order that they may shoot in secret One unspotted”. The bow he calls lyings in wait. For he that with sword fights hand to hand, openly fights: he that shoots an arrow deceives, in order to strike. For the arrow smites, before it is foreseen to come to wound. But whom could the lyings in wait of the human heart escape? Would they escape our Lord Jesus Christ, who had no need that any one should bear witness to Him of man?
“For Himself knew what was in man,” as the Evangelist testifies. Nevertheless, let us hear them, and look upon them in their doings as if the Lord knew not what they devise. The expression he used, “They have bended the bow,” is the same as, “in secret:” as if they were deceiving by lyings in wait. For you know by what artifices they did this, how with money they bribed a disciple that clave to Him, in order that He might be betrayed to them, how they procured false witnesses; with what lyings in wait and artifices they wrought, “in order that they might shoot in secret One unspotted.”
Great iniquity! Behold from a secret place there comes an arrow, which strikes One unspotted, who had not even so much of spot as could be pierced with an arrow. A Lamb indeed He is unspotted, wholly unspotted, always unspotted; not one from whom spots have been removed but that has contracted not any spots. For He has made many unspotted by forgiving sins, being Himself unspotted by not having sins. “Suddenly they shall shoot Him, and shall not fear.” O heart hardened, to wish to kill a Man that did raise the dead!
“Suddenly:” that is, insidiously, as if unexpectedly, as if not foreseen. For the Lord was like to one knowing not, being among men knowing not what He knew not and what He knew: yea, knowing not that there was nothing that He knew not, and that He knew all things, and to this end had come in order that they might do that which they thought they did by their own power.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)