American grammar has taken a hit in recent years and so the fine point of the difference between using I shall and I will has lost its punch. But in the Bible the difference is especially important because when God says He shall He means quite something difference from He will.
Will, as a verb, has two distinct meanings, often muddied together. Will can be a future event and a decision, opinion or plan such as, “I will walk more for health reasons.” Shall, however, means a decision or event is set in stone.
Example: The meeting will be at 8 p.m. Clearly the meeting has no mind of its own and cannot will something to happen. Will, is this case is an intention or a scheduling item referring only to the future.
The will of man is another, and more important use of the word. When someone says I have written my will, they mean that after they are dead others should follow through on their wishes. As anyone can testify, more often than not the will of the living prevails, and the inheritance may be entirely lost or stolen. Your will lasts only as long as you do. There is the will of the devil too. God speaks to this when the evil one gets uppity in Isaiah:
13 You thought to yourself, ‘I will scale the heavens,
I will raise my throne above God’s stars.
I will sit on the Mount of Assembly
far away in the north. I will ascend above the heights of the clouds;
I will be like the most High.
God’s response to Satan is “You SHALL be brought down to the pit. When God says shall, the issue is settled. It is going to happen. Man’s will and the devil’s will are temporary; God’s shall is forever.
Pay attention to this word shall in your Bible and see what God has to tell you.