Stand up when you see someone preaching in a mosque

This hadith is about the importance of standing while delivering a sermon in the mosque. Ka'b b. 'Ujra reported that he entered the mosque and saw Abd al-Rahman b. Umm Hakam delivering the sermon in a sitting posture. Upon this he said that it was not appropriate to deliver sermons while sitting as Allah has commanded us to stand when we see merchandise or sport and leave those who are preaching standing. This hadith teaches us that we should respect those who are preaching by standing up for them and listening attentively to their words instead of getting distracted by other activities or things around us. It also teaches us to be mindful of our actions as they can have an effect on others around us even if we do not intend it so.