'Understand' in the Bible

First of all, you must understand this: No prophecy in Scripture is a matter of one's own interpretation,

But these, as natural brute beasts, made to be taken and destroyed, speak evil of the things that they understand not; and shall utterly perish in their own corruption;

First of all you must understand this: In the last days mockers will come and, following their own desires, will ridicule us

The Lord does not delay His promise, as some understand delay, but is patient with you, not wanting any to perish but all to come to repentance.

He speaks about these things in all his letters in which there are some matters that are hard to understand. The untaught and unstable twist them to their own destruction, as they also do with the rest of the Scriptures.