The key of David has several facets. (Isa 22:22, and Rev 3:7). Among them are:
1) Knowledge of who those are "who claim to be of Judah, and are liars" (Rev 2:9 and 3:9)
and where they came from, and who they are today.
2) To Understand the 3 earth ages, and who the elect are, and why they are elect.
3) To know the difference between the houses of Israel, Jacob and Judah, as well as where they are today. Know who Esau
is today and the manner in which he will attempt to keep the promise made he in Gen 27:41
4) Know both who anti-christ is and the season of his appearance. Understand and identify his eight roles in the scripture.
Know that he (Satan) is coming before the true One, and will decieve all but the elect. Know many of the signs of his (satans)
coming, both what will precede, and what sort of miracles he will do. Know precisely how long he will reign.
5) Recognise and identify the 4 'horsemen' with the 4 hidden dynasties of economic, political, social and religious significance.
6) Understand the Word regarding God's plan to such a degree that you are both able and sure in judgement of traditions
of man, and able to discriminate to the degree that some idea is either worthy of further study, or fit only to be ignored.
7) Probably (surely) there are other facets, also.
With the knowledge as above, one is able with the help of the Holy Spirit to stand against the wiles of the false one,
and to fulfill the destiny they are appointed..
I am sure from reading some of your posts that you are at least passingly familiar with some or all of the above concepts.
If you would like to discuss any of the above, I can expound on what little I know and where in the Word I got it.