St. Matthew 12:20 = Isaias 42:3.
The Catholic Haydock Commentary quotes St. John Chrysostom (hom. xli) on this verse:
The bruised reed. The prophet here shews the mildness of our Saviour, who, though he could have broken them like a reed, and as a bruised reed, yet would not do it; and though he could have easily extinguished their rage and anger, yet he bore with it for a while, with singular clemency, till he should send forth judgment unto victory, i.e. till justice shall have appeared triumphant, till Christ shall have fulfilled all things, and raised his most illustrious trophy: till the Gentiles shall have placed their confidence in his most adorable name, and the Jews have no plea, notwithstanding their unparalleled obduracy, to make in reply.
St. Thomas Aquinas's Catena Aurea ("Golden Chain") cites more Church Fathers on this verse, such as:
St. Augustine: So He neither bruised nor quenched the Jewish persecutors, who are here likened to a bruised reed which has lost its wholeness, and to a smoking flax which has lost its flame; but He spared them because He was not come to judge them, but to be judged by them.
St. Hilary: Or, he means this bruised reed that is not broken, to shew that the perishing and bruised bodies of the Gentiles, are not to be broken, but are rather reserved for salvation. "He shall not quench a smoking flax, shews the feebleness of that spark which though not quenched, only moulders in the flax, and that among the remnants of that ancient grace, the Spirit is yet not quite taken away from Israel, but power still remains to them of resuming the whole flame thereof in a day of penitence.
St. Jerome, Ep. 121, 2: Or the reverse; He calls the Jews a bruised reed, whom tossed by the wind and shaken from one another, the Lord did not immediately condemn, but patiently endured; and the smoking flax He calls the people gathered out of the Gentiles, who, having extinguished the light of the natural law, were involved in the wandering mazes of thick darkness of smoke, bitter and hurtful to the eyes; this He not only did not extinguish, by reducing them to ashes, but on the contrary from a small spark and one almost dead He raised a mighty flame.
St. Remigius: … "He shall not break the bruised reed," refers to His shunning His persecutors that they might not be made worse…