Q:

必／会， 这个句子为什么用”必“？必 vs 会？ Why does this sentence use "必“？

我读圣经的时候看了这个：

你不要害怕，因为我与你同在；不要惊惶，因为我是你的神。我必坚固你，我必帮助你，我必用我公义的右手扶持你。（以赛亚书 41:10）

我看懂它的意思，可是我不看懂 “必”。我知道它想说“我会坚固你，我会，等等“，可是它为什么用“必”？我查资料了它和知道“必”的意思是“需要”或者“会”。”会“是比较简单的吗？还是是一样的？对不起我的中文不好！
I was reading the Bible and saw this:

你不要害怕，因为我与你同在；不要惊惶，因为我是你的神。我必坚固你，我必帮助你，我必用我公义的右手扶持你。（以赛亚书 41:10）
Fear not, for I am with you, be not afraid, for I am your God, I will (必）strengthen you， I will (必） help you, I will （必） uphold you with my righteous right hand. Isaiah 41:10

I understand the meaning, but I don't understand why 必 was used. I know the meaning is "I will strengthen you, I will, etc.", but I don't understand why 必 was used instead of 会. After looking it up, I understand 必 can mean "must" or "will", but is 会 less formal? Or are they the same and it's simply a matter of word choice?

A:

必 emphasises and reinforces much more the idea of definitive, firmness.
我会帮助你 means I will help you
我必会帮助你 means I will definitely help you
You would say 我必会帮助你 when you are 100% sure you will commit to help the person. 
You feel much more secure about the other person's commitment if the person tell you 我必会帮助你. 
必 also emphasises on the idea of success as in when you say 我必会帮助你, you are also quite sure that you can help the person successfully.  
You could say 我一定会帮你 to mean I will definitely help you. But you feel less secure about if the person can actually help successfully. 
God is all-powerful, hence he can use 必. You feel secure and confident in his presence and in this question, you feel secure and confident from his words when he tells you that he will help you. 

