I think one of the most frustrating things a submitting writer faces is how do you read those rejection letters? What exactly is an agent saying when she says that the book “didn’t grab her” or “the writing isn't strong”? Do you need to do revisions? Should you stop submitting? Or should you just ignore them all and carry on.
The truth is that these phrases are simply gentle ways for the agent to say “thanks, but no thanks,” and unless you know and understand exactly what an agent is saying to you I wouldn’t read it as a sign that revisions are needed. Maybe they are, maybe they aren’t, but unless you know what those revisions need to be (either from an agent’s feedback or your own evaluation) there’s really nothing you can do about it.
The reader who asked this question said that one of her fears is spending a year sending out what could possibly be a flawed manuscript. Well, the truth is that even agents spend time sending out “flawed” manuscripts, or at least manuscripts that don’t sell. This is why I encourage authors to work on something while submitting. Working on something fresh can help you worry less about the book that’s on submission and puts less pressure on that book. If it doesn’t sell and if it does have flaws, hopefully it can be okay if the next book is even better.