Accustom yourself not to be disregarding of what someone else has to say: as far as possible enter into the mind of the speaker.
What does not benefit the hive does not benefit the bee either.
If sailors spoke ill of their captain or patients of their doctor, who else would they listen to? Otherwise how would the captain achieve a safe voyage for his passengers or the doctor health for those in his care?
How many with whom I came into the world have already left!
In the first passage, Marcus seems to be saying, "try, as best you can, to understand what someone is saying." Listen to what they are actually saying and be mindful not to add on, to what they are saying, with your opinion. In my opinion, so much of what people say, is misunderstood because of added opinion. Listen to what others say; rephrase and listen again.
In the second passage, Marcus repeats what he has said before.
In the third passage, he seems to be alluding to the discipline of desire. We have to accept what the world and universe is telling us. If you won't listen to an expert, then who will you listen to? The ultimate "expert" is actual life - actual events in the world and universe. You must accept these things; you cannot reject events that happen to you. The expert doctor knows what's best for your health. The expert captain knows what's best for a safe voyage.
Finally, death becomes us all.