It's not faith. It's presumption.
And it's a sin...
Now let me state outright that planning is good, normal, and healthy. But I can and must say that when planning becomes presumption, we have crossed the line into sin. When things don’t unfold as we had assumed they would or as we had planned, it is easy to get angry or bitter against God or other people. But if we recognize that God is in control and we are not, it is much easier to be flexible and pliable to the plans of God as they unfold. I am not against long term thinking, mid-term planning, or short-term projections. Such are a necessary part of business and life in general. But any accomplished and honest businessman can tell you that one of the most important things about management is being willing to seize opportunities as they come which can and does result in deviating from the specifics of the plan at times. The same is true in the Christian life. We know the general direction we are to go. For example, we should read God’s Word, pray, train our children to obey the Lord, fellowship with other believers, love our spouses, etc. But I know I would drive myself crazy if I was trying to decide where my kids were going to go to college today. I don’t even know where they are going to go to kindergarten. When we start thinking that we have our future all lined up and figured out, we risk the sin of presumption. God doesn’t mind us planning and being wise stewards of time, energy, and resources. But what He doesn’t take glory in is us imposing our will upon Him such that we don’t remain pliable to His plans as they unfold tomorrow.
We are not allowed to worry about tomorrow (Matthew 6:34), and here in James we are told not to presume upon tomorrow. Frankly, as James alludes, we don’t even know if we will be alive tomorrow. We might go to bed tonight and never wake up. That is not meant to be a morbid thought, but it is meant to be a sobering thought. Christians are called to walk soberly because we have a sober calling (e.g. 1 Peter 4:7, 5:8, 2 Timothy 4:5). Life is short, our mission is clear, and our calling is serious. God wants us to daily take up our crosses, deny ourselves, and follow Him (Luke 9:23), regardless of what He ordains to come our way. He gives us daily bread for our daily needs (Matthew 6:11). Daily we need to seek our Lord for daily provision. Then tomorrow, we should do the same. Again, this does not negate planning, for choices we make today are often in light of consequences of the future. But the key is that we cannot presume upon certain future events unfolding in our lives on earth when we make our decisions today. We are not God, and such thinking is pure arrogance. It will only lead to stress and worry as we struggle and strive to make things fit exactly as we had envisioned them. God doesn’t want us to boast about anything, including our own power to control our own destinies. The key is that we must retain an attitude in our hearts which says, "If the Lord wills" (c.f. Paul in Acts 18:21). This is a humble, proper attitude before a Sovereign Lord which acknowledges that our days and times are in His hands, not ours.
The call isn’t necessarily to say "if the Lord wills" after everything we say or plan to do. It is not some magical charm as if there is power in the words. What God is after is a heart attitude that does not presume which would otherwise cause us to boast in our own power and self-sufficiency. He wants hearts that acknowledge that He is over all things, including our lives and including our tomorrows. If God wills, we will get married, have kids, get that job, sell that house, seal that deal, get that contract, etc. We might be good at what we do, but we are not God. We might be skilled or visionary, but we are not sovereign. We might be good as making things happen, but we are not all-powerful. God’s plans cannot be thwarted, but ours can be and regularly are. God doesn’t want us to presume upon our ability to carry out our vision and plans, but He does want us yield to His plans and purposes for our lives, whether at home, at work, at school, or anywhere and anytime. This is one of the predominant ways in which we fulfill God’s command in Proverbs 3:6 to acknowledge God in all of our ways. The result is that God will direct our paths, making our way straight. He will take us where He knows we ought to go if we let Him. Arrogance opposes God, and God opposes the arrogant (James 4:6). But He gives grace to the humble, to those who seek His will and yield to His leading.
Let us not grow arrogant and fall for the sin of presumption, but let us rather willingly and humbly follow God as He leads. Let us say with David, "My times are in Your hand" (Psalm 31:15).