In this glorious hadith, Muhammad teaches that the Creator of 2 Trillion Galaxies rejects your prayers if you fart.
In fact, Allah will forever reject your prayers after a fart until you properly perform wudu (ablution). This involves pouring water over various parts of your body, at least once and ideally three times for most parts, also rinsing your mouth and nose.
There are many things that Muhammad says nullify wudu. These include defecating, urinating, farting, sleeping (because you may have farted), eating camel meat, and touching your penis.
The problem with wudu is that it is nonsensical. It is an act depicting physical cleansing, but it doesn’t properly clean you. It avoids one’s private parts, but it’s the private parts that are the cause of needing wudu.
Acknowledging that, Muslims argue that, well, it “spiritually” cleans you, but any person—not obliged to obedience to Muhammad—would argue that meditation is a far better way of "spiritually" cleansing than washing your feet.
Ultimately, it boils down to: You do it because Muhammad said so. You do it because Muhammad says sins literally leave your body when you do it (Ibn Majah 282). You do it because Muhammad says the angels will stop praying for you if you don’t.
You do it because a sex-slave owner —who says girl's urine is worse than boy's urine and that Allah gives you 100 points for killing a gecko—told you to.