If you will please read the rest of your link, you see that it itself spells out that should is “properly” the past tense form of shall, which is itself a present tense verb. This is similar to how would is the morphological past tense form of the present tense verb will. Similarly with may and might.
English verbs have no morphological future form, not now, and not ever. You cannot change an English verb's form to make it a future tense verb the way you can change sing to sang or cry to cried when you create a past tense verb form. With the future, that is impossible, and always has been.
Instead of changing the form of the verb to express such things, English uses other words to convey that an event takes place at some time other than now. For example:
I see the doctor tomorrow at three.
By that tomorrow at three you can tell that the action is not taking place today, but in the future. The verb see does not change form, however. On the other hand, for the past, it does:
I saw the doctor yesterday at three.
There is nothing more to be done with that verb than see and saw, plus seen and seeing for participles. For anything else, you need other words because you cannot turn that verb into a future tense form.
Modalities
English has something better than future tense: it has modalities via modal verbs — which are something else altogether. Mode and tense are different things.
All English modal verbs have both an epistemic sense and a deontic sense. This instance of shall in your translation does ɴᴏᴛ simply indicate some future event in an epistemic way the way this one does here:
I shall have to give it another look.
Rather, this is the deontic modality of permission, of command, of inevitability — the one seen in:
You shall not pass!
So this is not “future tense”; it is a present tense modal verb being used in the deontic mode to indicate a special kind of future event.
The verb come is in the infinitive. We cannot use the past tense form came here, and since there is no future tense form for that verb (nor for any in English), we use a modal plus an infinitive instead to get much the same job done as a future tense would have.
Compared with real future tense
For an actual future tense example, since there is nothing in English, you need a language that had such a thing. Conveniently here, you could look at your verse’s Latin translation, since that language had a future tense. In the Vulgate, that verse runs like this:
Hoc autem scito quod in novissimis diebus instabunt tempora periculosa.
That verb instabunt is the third person plural future active indicative form of the verb insto. It’s a third person plural form to agree with tempora periculosa, “dangerous times”. But it is not present tense. It is future tense. If it had been in the present tense, it would have been instant, but by changing the tense of the verb from present to future tense, you get instabunt instead.
That’s how future tense works in languages that have such a thing: the verb’s inflection changes. You have to use a different word.
So why did the English translators choose a deontic modal instead of an epistemic modal for this verb? The answer to that can be found by examining the other verb in that sentence. Scito is a future imperative of the verb scio “to know”. It is not a normal present imperative, which would have been just sci (although this is a rarely used form) in the present imperative, not scito in the future imperative.
With the commanding verb in the future imperative, it therefore makes more sense to use the deontic modal shall here for the translation in the other clause rather than the more normal epistemic will. So you get shall come, a present tense verb being used in the deontic modality combined with another verb in the infinitive.
There’s more to it than this, but this should get you started.
