It is really important for me to know the truth.
The truth about what?
That's how I've come to know you. The more puzzled I am that you are willing to die on this hill.
What hill? God could not give a damn what I believe about cladistics and since I only care about what God thinks of me maybe you can do the math.
So what? Why does it matter if they are right, other than to bolster their ego?
I don't even have to read that. The titles only show that I am right. "Other Animals" and "Other Great Apes". That says that humans are animals and that humans are great apes.
It is almost unbelievable that anyone would care this much about being right, that they would not even care about anything else.
I conceded to humans are animals and humans are great apes but what difference does it make in the overall scheme of life?
Humans are a lot of other things but you don't even want to look at those because you are so obsessed with one thing.
It's not so much science we are discussing but logic. (And I know from past interactions that you care about being rational in your belief.)
Cladistics is an application of set theory which is an important part of logic.
You have to know that natural language is often ambiguous and that may be the case why you are confused here.
A is B can have the meaning of A = B (identity) or A ∊ B. As B in our case is a group (apes) and A is a subgroup(humans) it makes sense to say that humans are members of the greater group of apes. That doesn't mean that they are identical.
Understanding that will not necessarily make you a better person but it will make you a more rational person - if you are still interested in being rational in your beliefs. (A claim I have frequently heard but very rarely followed through.)
No, I do not need to know cladistics in order to be a rational person, and it certainly does not help me to be a more spiritual person, which is all I really care about. A need to be right is death to humility, which is one of the most important attributes of spirituality.