Of all the things that get ruined by a modern world obsessed with money, great art is the one that bothers Ezra Pound the most. For Pound, there's honestly not much point to life without beauty, and the main way we're able to get beauty into our lives (according to him) is through art. Pound makes no bones about it; if the world had always cared about nothing but money, we wouldn't have all of the beautiful art that has been passed down to us from centuries ago.
Lines 6-7: Toward the beginning of the poem, Pound implies that usury and the obsession with money weren't as much of an issue in the old days. But in modern times, these things have ruined art. He decides to show us just how much this is the case by claiming that in a world wit usura, "no man [would have] a painted paradise on his church wall" (6). This line is taken from the 15th-century French poet Francois Villon, whom Pound admired very much. Here, he basically says that people in finance don't care about anything but numbers, and this makes the world an impossible place to create great art.
Line 11: Pound gets a little obscure when he says that in a world with usura, "no man [sees] Gonzaga and his heirs and his concubines" (11). Here, he's referring to a painting by Andrea Mantegna called Gonzaga, His Heirs and His Concubines. Further, the man named Gonzaga who appears in the painting was a rich man who used his money to pay artists to create great art. In the modern world, Pound implies that you'd have a hard time finding a man like this.
Lines 12-13: Next, Pound claims that in a world obsessed with money, "no picture is made to endure or live with" (12). In other words, people don't make pictures hoping that they'll still be looked at after they're dead. They make pictures that'll sell really quickly. That's why you sometimes get great artists painting pictures of dogs and sailboats instead of what they'd really like to paint, because tourists and customers like to buy stuff that's "made to sell and sell quickly" (13).
Lines 28-36: In these lines, Pound just creates a list of great pieces of art and great artists (Pietro Lombardo, Duccio, Pier della Francesca, etc.) who flourished during a time when rich people were more than willing to spend money on great art, even though they never planned on selling the art or making a profit from it.
Lines 41-42: Continuing in the same vein he's been in throughout Canto XLV, Pound says that "cramoisi is unbroidered" (41) in a world with usura. Cramoisi is a type of French cloth that is beautiful, but fancy and painstaking to make. Which means that it doesn't get made in the modern age, because we're all about efficiency instead of quality.