How astonishing the believer's affair is! Indeed, all of his affairs are good, and this is for none but the believer

The Prophet (may Allah's peace and blessings be upon him) expresses wonder, by way of admiration, at the believer's affairs and conditions because all of his conditions are good, and this is for none except the believer. Whenever something good happens to him, he thanks Allah for it and gets rewarded for showing gratitude. If something bad happens to him, he shows patience and seeks reward from Allah and, thus, gets rewarded for showing patience. So, he gets rewarded in all cases.

1. The merit of showing gratitude in prosperity and patience in adversity is that whoever does this will attain goodness in both abodes. However, one who neither shows gratitude in the case of blessings nor patience in the case of calamities will miss the reward and incur sin.
2. The merit of Imān (faith) and the fact that reward in all cases is for none but for those who have faith.
3. Showing gratitude at times of prosperity and patience at times of adversity are from the believers' characteristics.
4. Belief in Allah's decree and predestination makes the believer perfectly content with all of his conditions, unlike the non-believer, who is constantly discontented when experiencing hardship, and if he receives a blessing from Allah Almighty, he becomes preoccupied with it and gets distracted from obeying Allah, let alone using such a blessing in disobeying Him.

صحيح مسلم (4/ 2295) (2999). بهجة الناظرين شرح رياض الصالحين، لسليم الهلالي (1/ 82). شرح رياض الصالحين، لابن عثيمين (1/ 197). نزهة المتقين شرح رياض الصالحين، لمجموعة من الباحثين (1/ 59).