Mu'jam al-Saghir

Hadith Commentary:
A person generally disobeys Allah Most High through the tongue and the private parts; guaranteeing these two means that he refrains from lewd actions and obscene speech.
The virtue of avoiding the extremely filthy acts associated with these two is that the Messenger of Allah (sallallahu alayhi wa sallam) has guaranteed Paradise for such a person.
Imam Bukhari (rahimahullah) has established the virtue of abandoning indecencies and evil deeds from this hadith.
And Allah knows best.

Hadith Commentary:
(1)
Among the human body parts, after the tongue, the organ whose protection holds special importance is a person's private parts. Therefore, in this hadith, the Messenger of Allah (sallallahu alayhi wa sallam) has mentioned the guarantee of both these organs: that whoever takes responsibility for safeguarding his tongue and restraining the desires of his self, I guarantee Paradise for him on behalf of Allah, the Exalted.

(2)
It should also be kept in mind that the addressees of such statements of the Messenger of Allah (sallallahu alayhi wa sallam) are those believers who fulfill the fundamental requirements of faith. On one occasion, a companion (radi Allahu anhu) asked the Messenger of Allah (sallallahu alayhi wa sallam) about salvation, so he replied:
"Control your tongue."
(Musnad Ahmad: 259/5)

Explanation:
1:
Since the tongue and the private parts are the primary centers from which sins originate,
therefore, it is especially necessary to safeguard them.
The importance of this can be gauged from the fact that the Prophet (sallallahu alayhi wa sallam) has guaranteed Paradise for those who guarantee the protection of these two.