Enemies Without and Within

Vos autem, carissimi qui hanc fidem habetis vel qui nunc novam habere coepistis, nutriatur et crescat in vobis. Sicut enim venerunt temporalia tanto ante praedicta, venient et sempiterna promissa. Nec vos decipiant vel vani Pagani, vel falsi Iudaei, vel fallaces haeretici, nec non in ipsa Catholica mali Christiani, tanto nocentiores, quanto interiores inimici. Quia et hinc ne perturbarentur infirmi, prophetia divina non tacuit, ubi loquens in Cantico canticorum sponsus ad sponsam, id est, Christus Dominus ad Ecclesiam: Sicut lilium, inquit, in medio spinarum, ita proxima mea in medio filiarum. Non dixit, in medio extranearum; sed: In medio filiarum. Qui habet aures audiendi, audiat; et dum sagena quae missa est in mare, et congregat omnia genera piscium, sicut sanctum loquitur Evangelium, trahitur ad litus, id est, ad saeculi finem secernat se a piscibus malis, corde, non corpore; mores malos mutando, non retia sancta rumpendo: ne qui nunc probati reprobis videntur esse permixti, non vitam, sed poenam reperiant sempiternam, cum coeperint in littore separari. Sanctus Augustinus Hipponensis, De Fide Rerum Quæ Non Videntur

But you, beloved, who have this faith, or who have begun now newly to have it, let it be nourished and grow in you. For as things temporal have come about which were long foretold, so will come things eternal which have been promised. Nor let them deceive you, either the vain pagans, or the false Jews, or the deceitful heretics, or, within the Catholic Church itself, evil Christians, who are much  more hurtful insofar as they are closer enemies. And lest because of this the weak should be troubled, Divine Prophecy has not been silent, for in the Song of Songs the Bridegroom speaking to the Bride, that is, Christ the Lord to the Church, says, 'As a lily in the midst of thorns, so is my dearest in the midst of the daughters.'1 He did not say, 'in the midst of those who are without', but, 'in the midst of daughters.' 'Whoever has ears to hear, let him hear.'2 And while the net which is cast into the sea, and gathers together all types of fish, as the holy Gospel says, is being drawn to the shore, that is, to the end of the world, let him separate himself from the evil fishes, in heart, not in body, by changing evil ways, not by breaking sacred nets, lest they who now seem approved mixed with the reprobate, meet with, not life, but punishment everlasting, when they begin to be separated on the shore. Saint Augustine of Hippo,Concerning Faith of Things Not Seen 1 Song 2.2 2 Mt  11.15