Final answer:
The verse Hebrews 11:6 states that one must believe that God exists and that He rewards those who earnestly seek Him, emphasizing His nature as a responsive and benevolent deity.
Step-by-step explanation:
According to Hebrews 11:6, the main answer to what one must believe in addition to God's existence is c) That He rewards those who seek Him. This belief is crucial for he who comes to God, for it is faith in His benevolence and the idea that seeking God is not in vain. Explanation in more than 100 words: In the context of the Judeo-Christian-Islamic tradition, God is perceived as a deity with attributes of being supreme, all-powerful, and all-good. This is important because it pertains to the character of God and what believers are expected to acknowledge about God's nature. Specifically, believing that God is and that He is a rewarder of those who diligently seek Him encapsulates a hopeful and trusting aspect of faith. It suggests a personal relationship with a God who is aware of and responsive to the quest for spiritual connection and righteousness. Conclusion: Hence, it is essential to acknowledge God's character not only as the sovereign creator but also as an active participant in the human spiritual journey, rewarding those who earnestly pursue Him.