This is the second of three paragraphs on the phrase, "immediately after the oppression of those days". In the first of these three, He talks a bit about the problem with some of the ignorant clergy, as opposed to the good clergy.
In this paragraph, He continues this by pointing out that this is a theme found throughout all of history. As the people find themselves lost, without any clear understanding of where to seek God, as the ignorant are in the positions of power and authority, as darkness overshadows all regions, then the Messenger appears.
In some ways, this is like a heartbeat. It is regular, continual and systematic. We seem to have the regular infusion of divine Knowledge which gives life to all humanity, just like the regular infusion of blood into our body, pumped by the heart, gives life to our body.
One thing that stands out for us is the phrase, "the ways unto the attainment of God have multiplied". We are reminded of Jesus saying "“I am the way and the truth and the life. No one comes to the Father except through me." The only way to God is through the Messenger, whether that be Muhammad or Jesus, Buddha or Moses, Baha'u'llah or the Bab. And yet at this time in history, the time that calls for a new Messenger, the clergy misdirect people to look to them, the clergy instead of the Messengers, and their feeble interpretations of the Word of God.
People try to be obedient, follow the clergy, of which there are too many, and are in obvious confusion. They know that what these people say doesn't make sense. Perhaps this is one of the reasons why so many people today disregard religion altogether. They see the hypocrisy and ignorance and figure that the whole thing must be junk.
It is sort of like those Babis who saw Mirza Yahya and his claim to be a Manifestation, and figured, "If this yahoo is making a claim, then I must be the real Messenger." Remember how many claims were made before Baha'u'llah made His? Many dozens. Compared to Mirza Yahya, it just seems to make sense. But when these people saw the true majesty of Baha'u'llah, they understood their iniquity and became Baha'i.
But going back to the passage, this cycle still makes sense. After all, if the people were rightly guided, and could easily find the path to God, why would there need to be a new Messenger? How can the sun rise in the morning if it hasn't set the night before?
We could talk more about this here, but really, part 2 of 3 is always is hardest to explore. Baha'u'llah concludes His look at this phrase in the next paragraph, and so shall we.