On Moths and Rust

St. Ambrose of Milan ca. 338-397

[T]he Gospel was written to Theophilos, i.e., to him whom God loves. If ye love God, it was written to you, discharge the duty of an Evangelist. Diligently preserve the pledge of a friend in the secrets of the Spirit. Frequently consider, often discuss the good things committed to thy trust by the Holy Spirit Who is given to us (2 Tim. 1:14). Faith is due first to a pledge; diligence follows faith, lest moth or rust consume (cf. Mat. 6:19-20) pledges committed to you; for what is committed to you can be consumed. The Gospel is a fine pledge, but see neither moth nor rust consume it in your spirit. Moths consume if ye poorly believe what ye have well read. A moth is a heretic… a moth… tears the garment… A moth is to know Christ without faith in His Godhead or in the Sacrament of His Body… But those who are of God keep the faith and therefore cannot suffer from the moth which divides the garment. For everything which is divided within itself, like the kingdom of Satan, cannot be everlasting (cf. Mat. 12:25). Moreover, it is the rust of the spirit when the keenness of religious intention is dulled by the defilements of worldly desires or the purity of the faith is stained by a cloud of unbelief. Rust of the mind is a desire for the familiar; rust of the mind is carelessness; rust of the mind is longing for honors, if the greatest hope of the present life is set thereon. And, therefore, let us turn toward the Divine, and let us sharpen our character; let us drill our disposition, so that we may have that sword which the Lord bade us sell our garment and buy (Lk. 22:36), always ready and shining, as if sheathed in the scabbard of our mind. For the soldiers of Christ must always have strong spiritual weapons for the destruction of fortifications against God (2 Cor. 10:4), lest when He come, the Leader of the Heavenly Host (cf. Josh. 5:13; Lk. 2:13), offended by the dullness of our weapons, separate us from the company of legions. (Exposition of St. Luke, Bk. 1: 12-14)