Here is a second warning from Baha'u'llah about how we are to approach this paragraph from Matthew, and, indeed, all the Sacred Texts: We should recognize that the laws are regenerated and renewed as needed in each Age. We will also need to submit to these new laws, and that might be difficult for us, as it is not easy to move from our old set of traditions to a new one. It is good to remember that Jesus changed some laws from the dispensation of Moses, the law of the Sabbath being one example, and we can see the effect it had at the time.
We see this as another caution. While it is acceptable, and sometimes preferable, to read the words literally, we should be cautious not to do so to an extreme. Baha'u'llah does not seem to be condemning the people of that day for using a literal interpretation, but instead for trying to impose it upon others. By doing so, they were moving beyond the bounds of moderation and humility, forgetting that they could still learn more.
This pattern, which we see here between the followers of Jesus and those of Muhammad, continues that which we had seen earlier in this Book.
Baha'u'llah, indeed all the Messengers of God, has told us repeatedly that God is exalted above the Manifestations and They do His bidding; They are all His servants. They are, as the Bab says, but a ring upon His finger. It is to God that we must become attached, and not the Words. This is the true meaning of detachment. "Forget all save Me, and commune with my Spirit".
Many Jews denied Jesus because He taught something other than what was in the Tanakh. Many Christians denied Muhammad because He taught something other than what was in the Gospels. Baha'u'llah is cautioning us not to fall into the same pattern. He specifically tells us to approach with a humble mind the true meaning of these words from every Manifestation, not just the Messenger of God we adhere to. Looking back on this pattern we should be able to identify this lack of humility in the mind.
This is a very important point to us, for it encourages us to keep an open mind about how we read things. There are some who are, of course, against this, as they see it as somehow weakening their faith. But what they fail to realize is that exploring the Writings from many points of view allows us to see where our faith, or reasoning, is weak. This type of exposure allows us to see how to strengthen our faith by reinforcing those areas of doubt. This whole Book, after all, is called the Book of Certitude, so it should not come as a surprise that we find this in here.