What is the meaning of hadith Sahih al-Bukhari 23?

Sahih al-Bukhari 23 : > **Narrated Abu Said Al-Khudri:** > > Allah's Messenger (ﷺ) said, "While I was sleeping I saw (in a dream) > some people wearing shirts of which some were reaching up to the > breasts only while others were even shorter than that. Umar bin > Al-Khattab was shown wearing a shirt that he was dragging." The people > asked, "How did you interpret it? (What is its interpretation) O > Allah's Messenger (ﷺ)?" He (the Prophet (ﷺ) ) replied, "It is the > Religion." (Religion is written with capital 'R', I think it is referring to Islam, arabic "deen"?) **What's the meaning of this hadith? Why is Allah's Messenger (ﷺ) interpreting wearing clothes in his dream to be Religion? What's the meaning of sizes of the clothes? Why Umar bin Al-Khattab was mentioned, not somebody else?** Is there any more explanation to this Hadith?