You can divide this sentence into two separate clauses.
The dependent clause, which provides the reason, is:
To understand the importance of this event
while the independent (statement) clause is:
you should know all the facts
Identifying these two separate clauses, it is then clear that a comma should be introduced between them, by standard rules.
Hence it's most correct to write:
To understand the importance of this event, you should know all the facts.
"As well as" means "in addition to"--it does not mean "and."
You would say
The teacher and the students are busy
but phrases such as together with, as well as, and along with do not function like and, that is, they do not create compound subjects.
And, you should include commas:
The teacher, as well as the students, is busy
This is because "as" (as well as), "to" (in addition to), and "with" (together with, along with) are prepositions and what follows them is not a subject, but rather an object (of the preposition). Hence, anything following these phrases does not affect the conjugation of the verb. Many people find this difficult to digest, and often it is better to recast the statement--by replacing "as well as" with "and," for example, or saying
The teacher is busy, and so are the students
or some such.
As for "Horse is a faithful animal," that is an entirely different question, and deadrat explains nicely above.
Best Answer
There is nothing I can see wrong in the syntax of that stanza. In fact, unlike much poetry, there is no serious lexical ambiguity; and with a single comma it would render just fine as a prose sentence:
Take "that sturdy assertiveness that walled England" to mean "the trait that formed a wall around England, which I will call 'sturdy assertiveness'" ... and thus shielded [as I am from such assertiveness], the noise of traffic in my mind becomes still.