question #1 Sahih Muslim 608c, Book 5, Hadith 211 : What is the significance of completing a rak’ah before the setting or rising of the sun in terms of fulfilling the prayer obligation?

The Messenger of Allah (ﷺ) said: He who finds (gets) a rak’ah of the afternoon (prayer) before the setting of the sun, he in fact gets (the full prayer), and he who gets a rak’ah of the morning (prayer) before the rising of the sun he in fact gets (the full prayer).