Allusions help the reader visualize what is happening by providing a picture in the reader's head. The reader also must be aware of the allusion and must be familiar with what it alludes to.
“In a very few hours I arrived in a city that always makes me think of a whited sepulcher.”
A "whited sepulcher" is a referring to Matthew 23:27-28 in the Bible when he says "You are like whitewashed tombs, which look beautiful on the outside but on the inside are full of the bones of the dead and everything unclean."
A sepulcher is a type of tomb that is decorated on the outside but is very bare on the inside.
"In this way the moons and the seasons passed. And then the locusts came. It had not happened for many a long year. The elders said locusts came once in a generation, reappeared every year for seven years and then disappeared for another lifetime. They went back to their caves in a distant land, where they were guarded by a race of stunted men. And then after another lifetime these men opened the caves again and the locusts came to Umuofia."
In the Book of Exodus, one of the 10 plagues was the Plague of Locusts. The lord says to Moses, "Stretch out your hand over Egypt so that locusts swarm over the land and devour everything growing in the fields, left by the hail."