Rasulullah (sallallahu ‘alaihi wasallam) has mentioned, “Whoever guarantees me (that he will safeguard and protect) that which is between his jaws and that which is between his legs, I will guarantee him Jannah.” (Saheeh Bukhaari #6474)
Safeguarding that which is between one’s jaws refers to two things. It refers to one being cautious in his speech i.e. abstaining from backbiting, lying, vulgar speech, speaking of things that are futile, etc., and it also refers to one ensuring that he only consumes halaal. Safeguarding that which is between one’s legs refers to one safeguarding his private parts i.e. abstaining from zina and all other sins of lust. (Mirqaat vol. 8, pg. 559)
If we have to ponder and reflect, we will realize that many, if not most of our sins and problems are related to either our speech or lust. Hence, if a person can exercise control over these two aspects, he will be able to eliminate most of the sins in his life and will thus be guaranteed Jannah by none other than Rasulullah (sallallahu ‘alaihi wasallam).