The sentence you are quoting is the first sentence of the Shema, namely:
שְׁמַ֖ע יִשְׂרָאֵ֑ל יְהוָ֥ה אֱלֹהֵ֖ינוּ יְהוָ֥ה ׀ אֶחָֽד׃
And the essence of your question is, "I noticed the verse doesn’t state: “HaShem Hu Echad”, but only “HaShem echad” why is this?"
This really relates more to reading without the cantillation. In the sentence, the Mercha, which is also known as Ma'arich, under the letter Vav in the first appearance of G-d's name (יְהוָ֥ה), extends that word to the word which follows it, namely Our G-d. The meaning here in translation is:
(this particular) four letter name which we associate with our G-d...
The letter Heh of the word, Our G-d has Tifcha under it (אֱלֹהֵ֖ינוּ), which has a connotation of joining to the word which precedes it and also to closing the phrase. It serves sort of like a comma in English.
So together, the phrase means this four letter name which we associate to our G-d, (that/the) four letter name of G-d...
The emphasis here is that there is a distinction between our G-d, meaning G-d at His essence, and His name.
There are many different concepts discussed in the literature of the Torah explaining the many facets of these concepts. But on the simplest level, G-d at His essence is what we recall from the giving of the Torah at Sinai. We saw no form, etc. G-d at His essence transcends all of creation in every sense.
And yet, we have been given names that we are to associate with G-d. One of them that is particularly associated to the Jewish people is the four letter name in this sentence like is emphasized in Shemot 3:13-15.
And this name is comprised of four letters which have different shapes, values and sounds. This could imply that G-d, at His essence, also has these distinctions in some way because it is His name.
The sentence then continues (after the comma/pause from the Tifcha mentioned above) by repeating that same four letter name associated with G-d and has a Munach l'Garmeh after it, (which implies another rest/separation point from the word which follows which completes the thought) and states it (meaning this name) is one.
In terms of understanding the Munach l'Garmeh, consider it similar to a semicolon. It's a pause between two main clauses and is more than a simple comma. In this case, the first clause is HaShem is our G-d. The second is HaShem is one.
This has multiple meanings. It means that this name itself is one, contrary to what we might think because we see that it is comprised of individual letters. And this is similar to the idea of your body being comprised of many limbs. But the individual limbs of ones body are all a single being. So too here, these four letters are to be understood as a single being/concept.
But it also means that this name which we have been told to associate with G-d at His essence (and which could be thought of as separate and distinct from G-d), is one with His essence! And that is a true wonder and something impossible to truly comprehend. That we are to accept that this name is one in the same way that we are taught that G-d at His essence is one, transcending all aspects of creation with an absolute simplicity.