This verse, clearly humorous, may seem out of place in what the KJV translates as an angry diatribe, but it fits perfectly into the entertaining arguments that Jesus actually was making when correctly translated. This is the second time that he uses the name, "blind guides," in this section. Three of the words, "gnat," "strain," and "swallow," are only used by Jesus here. The "gnat" and "camel" both representing violations of the law, but contrasting their size.
The issue here is that Jewish law forbids eating most flying insects, except those like grasshoppers and crickets. According to Jewish law, camels are prohibited as food just like flying insects. As we saw in Matthew 19:24, the camel is Jesus's go-to image for describing a large size.
The language is straightforward, but the word translated as "swallow" literally means "drink down." This makes the joke more clear since no one drinks a camel.