Never Impossible

The D&D, the core mechanic of the game is the "check." To "make" or "roll" a check, one rolls a twenty-sided die, adds and/or subtracts numbers based on their character's stats and the circumstances, and compares the total against the DC, or difficulty, of whatever they were trying to do. For example, if you wanted to climb a tree with a climb DC of 10, and you get +3 to the check because you're better at climbing than most people are, you would need to roll a 7 or higher because 7+3=10.

Given that the die only has twenty sides, and a character's modifiers provide only a limited bonus, it's entirely possible for certain tasks to be impossible for certain characters. For example, if the character with +3 to climbing tried to climb a sheer wall with a climb DC of 25, they literally would not be able to do it, because even if they rolled the highest number they could roll, 20, their total, 23, would be less than the DC, 25.

This makes sense, because in life, there are some things that are also literally impossible. A person couldn't jump across the English Channel or the Grand Canyon, no matter how good at jumping they are. Their modifiers could not be high enough to successfully make that check. Thankfully, we'll never have to.

God will never ask us to do anything that is literally impossible. He will only ever ask of us what we are capable of doing. Society, our inner perfectionists, or even leaders in the church may ask us for more than we can do, but God won't. What God asks is never impossible, no matter how impossible it may seem. This is partly because only God knows the exact difficulty of what He asks us to do, and we tend to overestimate it. He also knows exactly what we're capable of, and we tend to underestimate ourselves. But, I'll admit, it's also partly because when our best effort isn't good enough, and what He wants us to do is important to Him, He adds enough of a circumstance bonus to make up the difference.

Just as the +3 climber could climb up the DC 25 wall if he got a +2 circumstance bonus and a really lucky roll, we also can do anything that God asks us to do, and luck won't have anything to do with it. In life, the main variable isn't luck; it's effort. When God asks us to do something, it will always be worthwhile to put in the effort, because God will never ask us to do anything that is literally impossible to do.