Translation:

124. Whenever there cometh down a Surah some of them say: "which of you has had his faith increased by it? Yea those who believe their faith is increased and they do rejoice.

Notes (Tafseer)

1375. The incompatibility of Unfaith and Faith are contrasted in this section in respect of revelation and the divine teacher. The Unbelievers laugh at revelation, and say to each other mockingly: "Does this increase your faith?" To the Believer every new aspect of Allah's truth as revealed increases his faith, and wonder, and gratitude. He rejoices, because he gets added strength for life and achievement.