That thou mightest know the certainty of those things, wherein thou hast been instructed
Luke 1:1 Forasmuch as many have taken in hand to set forth in order a declaration of those things which are most surely believed among us, 2 Even as they delivered them unto us, which from the beginning were eyewitnesses, and ministers of the word; 3 It seemed good to me also, having had perfect understanding of all things from the very first, to write unto thee in order, most excellent Theophilus, 4 That thou mightest know the certainty of those things, wherein thou hast been instructed.
The Bible is the more sure word of prophecy.
This word translated "certainty" is used three times in the New Testament. This is the first use. The second is also by Luke in the book of Acts, the prison was shut up with all "safety", the same word that we are translating as certainty here. The final example is by Paul in 1 Thessalonians "when they say peace and safety". Again, the word translated "safety" is the word here for certainty. The word means certainty, undoubted proof, security from enemies and danger, hence safety.
The Bible is the undoubted truth, when Antichrist tells you that he has the undoubted truth you should know it is a trap, a snare.