KNOW THAT IT is mustaḥabb for anyone who addresses a group of people or imparts knowledge to them to be moderate and not to make it lengthy, lest they become bored or annoyed and the sweetness and respect be removed from their hearts, and lest they come to dislike knowledge and listening to the good and thus fall into danger.
We relate in the Ṣaḥīḥs of al-Bukhārī and Muslim that Shaqīq ibn Salamah related: “‘Abdullāh ibn Mas‘ūd 
used to remind us [about aspects of the Dīn] every Thursday. A man said: ‘Abū ‘Abd ar-Raḥmān, I would like it if you would remind us every day.’ He replied: ‘What prevents me from doing so is that I do not want to bore you. I admonish you as frequently as the Messenger of Allah 
used to admonish us, fearing that we might become bored.’” [1].
used to remind us [about aspects of the Dīn] every Thursday. A man said: ‘Abū ‘Abd ar-Raḥmān, I would like it if you would remind us every day.’ He replied: ‘What prevents me from doing so is that I do not want to bore you. I admonish you as frequently as the Messenger of Allah used to admonish us, fearing that we might become bored.’” [1].We relate in the Ṣaḥīḥ of Muslim that ‘Ammār ibn Yāsir 
reported: “I heard the Messenger of Allah say: ‘Making the ṣalāh long and the khuṭbah short is a sign of a man’s [good] understanding, so make the ṣalāh long and the khuṭbah short.’” [2].
reported: “I heard the Messenger of Allah say: ‘Making the ṣalāh long and the khuṭbah short is a sign of a man’s [good] understanding, so make the ṣalāh long and the khuṭbah short.’” [2].I say that ma’innah, ‘sign’, is written with a mīm with a fatḥah, then a hamzah with a kasrah, and then a nūn with a shaddah, and means ‘a sign that shows his understanding (fiqh)’.
We have related from Ibn Shihāb aẓ-Ẓuhrī, may Allah have mercy on him, who said: “If a gathering grows lengthy, Shayṭān has a share in it.”
References
[1] Al-Bukhārī (70) and Muslim (2821).
[2] Muslim (869) and Abū Dāwūd (1106).