"Also keep back Your servant from presumptuous sins; let them not rule over me; then I will be blameless, and I shall be acquitted of great transgression." (Psa. 19:13).
Pre sump' shun: Assuming an action is true or permissible without biblical warrant. Nadab and Abihu assumed God would accept their incorrectly measured incense (Lev. 10:1-2; Exo. 30:34.); Uzzah assumed God wouldn't mind if he kept the ark from falling (2 Sam. 6:6-7); Israel assumed God would give them victory against the Philistines because of the ark's presence (1 Sam. 4:3-11); Jewish businessmen assumed God would extend their lives another year to make money (Jam. 4:13-17); et cetera. The casualty list reads like a phone book of the people who presumed on God with dreadful consequences. Every sin is rebellion against God, but presumption super-sizes the evil (Num. 15:30-31).
Presumptuous sin cuts many ways. You can presume on the goodness of God and turn His grace into licentiousness -- assuming the mercy He gave yesterday is what He'll give today (Jude 4). Or you can presume and turn God's grace into legalism -- assuming the works you do today will satisfy God's holiness tomorrow (Matt. 7:22-23). Both seek to test the Lord, the former His goodness in order to sin, the latter His righteousness in order to boast.
Two characteristics of presumption compared to faith: First, presumption starts with an assumption; faith starts with a promise. Those who sit on a premise instead of standing on a promise, slip over a precipice. Faith says God will "give us this day our daily bread"; unbelief says He won't; doubt says He might; but presumption believes the bread must be hot and buttered -- an assumption. It might be, but God's under no obligation. Abraham could sacrifice Isaac because God said in "Isaac" your seed shall come -- a specific name attached to the promise (Heb. 11:17-19).
Second, presumption seeks to manipulate the outcome; faith waits patiently on the Lord (Heb. 6:15). Whether it's Hagar being given to Abraham to bring about the promised seed, Rebekah deceiving Isaac to fulfill Jacob's destiny, or Moses murdering an Egyptian to help free his brethren, manipulation never advanced God's promises, only hindered them. Faith knows that God's will done God's way will never lack for God's supply.
Don't presume on God. It's fatal. If faith is the assurance of things hoped for, presumption is the controlling of things wished for -- an assumption many in hell now realize.