Translation:

4. It is He who sent down Tranquillity into the hearts of the Believers that they may Add Faith to their Faith; for to Allah belong the Forces of the heavens and the earth; and Allah is full of Knowledge and Wisdom;

Notes (Tafseer)

4869. The results were achieved by tranquillity, calmness, and cool courage among the 1400 to 1500 unarmed men who accompanied the Prophet to Hudaibiya and who were threatened with violence by the excited Quraish leaders of Makkah.

4870. It is a casuistical question to ask. Are there degrees in Faith? The plain meaning is that believers will see one Sign of Allah after another, and with each their Faith is confirmed. During all the long years of persecution and conflict they had Faith, but when they see their old enemies actually coming out to negotiate with them, their Faith is justified, fulfilled, and confirmed: and they turn in gratitude to Allah.

4871. There are visible forces which you see in the physical world. Men fight with armed forces, and the Muslims had to defend themselves with arms also, and not without success.