In Carm. 73, a short elegiac poem, Catullus writes:^[1]

Stop wanting to earn any thanks from anyone

Or thinking someone can prove true.

Ingratitude is all. Kindness counts for nothing.^[2]

No, it’s even tiresome and does harm,

As I have found, whom no one pushes harder or more harshly

Than he who lately called me “one and only friend.”^[3]

It is a pessimistic poem about the fickleness of man, a poem about ingratitude and betrayal, and Martin Luther quotes from it in his 1532 commentary on Ecclesiastes (Annotationes in Ecclesiasten). Discussing Ecclesiastes 9:2-3 (“All things comes alike to all: there is one event to the righteous, and to the wicked; to the good and to the clean, and to the unclean; to him that sacrificeth, and to him that sacrificeth not: as is the good, so is the sinner; and he that sweareth, as he that feareth an oath. This is an evil among all things that are done under the sun, that there is one event unto all: yea, also the heart of the sons of men is full of evil, and madness in in their heart while they live, and after that they go to the dead,” KJV), Luther writes:

Again, we see the copious speech of Solomon, as if he should say: “The world is absolutely restless and ungrateful [ingratus], there is no remembrance of good things as there is of evil.” This, again, must be understood in relation to the world, not in relation to God. While they live, the righteous are scorned before the world and in the world. But before God they do well, as he said earlier: “He who fears God will do well.” But the world gives the same reward to the good and the evil. “Ingratitude is all. Kindness counts for nothing” [Omnia sunt ingrata. Nihil est fecisse benigne].^[4] “This, therefore, is the worst of all the things that occur under the sun.”^[5] That is, the human heart is too weak to be able to bear this perversity of the world. Those who do not have the fear of the Lord cannot patiently endure this ingratitude, and likewise the fact that no difference is made between the good and the evil, bur rather the same thing happens to all.^[6]

Notice how Luther uses the quotation from Catullus: he sets next to a quotation from Solomon, as if to say that the two are in harmony. Catullus gives the description of the world, and Solomon provides the judgment or evaluation of that description. Catullus is not praised here for knowing how things stand before God; but as far as understanding the ways of this world goes, his vision is keen.