With regards to the description of ‘Eesaa ‘alaihissalaam being described as “His Word which He conveyed to Maryam”[1]  the Shaykh Muhammad ibn Saalih al ‘Uthaymeen rahimahullaah states:

Allaah applied the (term) “Word” to him because he ‘alaihissalaam was created by means of a word. So the hadeeth is not taken upon its apparent (literal) meaning, since ‘Eesaa ‘alaihissalaam was not a word because he used to eat and drink and pass urine and open his bowels. And all the (usual) human situations would occur to him.

Allaah, the Most High, states:

Indeed the example of ‘Eesaa with Allaah is just as the example of Aadam. He (Allaah) created him from dust then He said to him, “Be!” and he was.
Soorah aale ‘Imraan (3) aayah 59

 And ‘Eesaa ‘alaihissalaam was not the Word of Allaah because the Speech of Allaah is an Attribute existing with Him and not separate and distinct from Him.

As for ‘Eesaa, then he was a being separate and distinct from Allaah subhaanahu ; he would come and go and eat food and drink.

(Al qawl ul mufeed (1/73) of Shaykh Muhammad ibn Saalih al ‘Uthaymeen rahimahullaah, translated by Nasser ibn Najam)

[1] Hadeeth reported by Al Bukhaaree (4453) and Muslim (28)

With regards to using the name “Muhammad” when referring to the Messenger of Allaah sall Allaahu ‘alaihi wa sallam, Shaykh Muhammad ibn Saalih al ‘Uthaymeen rahimahullaah states:

And his (ibn Mas’ood radi Allaahu ‘anhu) statement:

Whoever wishes to look at the wasiyyah (emphasised command) of Muhammad sall Allaahu ‘alaiyhi wa sallam….

 Meaning: the Messenger of Allaah Muhammad ibn ‘Abdillaah al Haashimee al Qarashee sall Allaahu ‘alaihi wa sallam.

And this expression from ibn Mas’ood shows the permissibility of the like of it, such as for example:
“Muhammad, the Messenger of Allaah sall Allaahu ‘alaihi wa sallam said….”
and:
“The wasiyyah of Muhammad sall Allaahu ‘alaihi wa sallam….”

 And this does not contradict His statement, He the Most High:

<<Do not make the du’aa (calling) of the Messenger amongst yourselves like your calling one of another…>>
Soorah an Noor (24) aayah 63

 – because the du’aa of the Messenger here means munaadah (calling out to him). So do not say when calling out, “O Muhammad!” Rather say, “O Messenger of Allaah!”

As for informing (about something) then it is more encompassing than the issue of seeking (something from a person), so it is permissible for you to say, “I am a follower of Muhammad sall Allaahu ‘alaihi wa sallam,” or “O Allaah, send salaat upon Muhammad” or the like of that.

(Al qawl ul mufeed (1/44) of Shaykh Muhammad ibn Saalih al ‘Uthaymeen rahimahullaah, translated by Nasser ibn Najam)

With regards to the use of the singular at times and the plural at other times in Allaah’s addressing the people in the Qur-aan, Shaykh Muhammad ibn Saalih al ‘Uthaymeen rahimahullaah states:

And the address in the aayah is to the Prophet sall Allaahu ‘alaihi wa sallam but He said:

<<Wa qadaa rabbuka allaa ta’budoo illaa iyyaahu…>>

meaning:

<<And your (in the singular form) Lord has decreed that you (in the plural form) worship none except Him alone…>>
Soorah al Israa (17) aayah 23

And He did not say, that you (singular) worship none.

And the like of this in the Qur’aan is His statement, He the Most High:
<<O Prophet, when you (in the plural form) divorce the women…>>
Soorah at Talaaq (65) aayah 1

Therefore the first address is to the Messenger sall Allaahu ‘alaihi wa sallam and the second is general (to the people).  So what is the benefit behind this changing of the manner (of addressing)?

1) To draw attention, because getting the attention of the person being addressed is something desired by the one speaking. And this occurs here by changing the manner (of addressing).

2) That the Prophet sall Allaahu ‘alaihi wa sallam was the leader of his nation. And the address directed to him was directed to all of his nation.

3) An indication that whatever the Messenger sall Allaahu ‘alaihi wa sallam is addressed with, then it is for him and for his nation – except for something where there is a proof that it is specifically for him.

4) And in this aayah in particular, there is an sign that the Prophet sall Allaahu ‘alaihi wa sallam was one who was under the control of the Lord, and not (himself) a Lord and Nurturer – a servant, and not one who is to be worshipped.  So he comes under His statement:

<<…that you (in the plural form) worship..>>

And sufficient for him in nobility is that he be a servant of Allaah, the Mighty and Majestic.

(Al qawl ul mufeed (1/32 to 33) of Shaykh Muhammad ibn Saalih al ‘Uthaymeen rahimahullaah. Translated by Nasser ibn Najam)

With regards to the hikmah behind the sending of the Messengers,
Shaykh Muhammad ibn Saalih al ‘Uthaymeen rahimahullaah
states:

So a messenger was sent to every nation from the time of Nooh up till the time of our Prophet Muhammad sall Allaahu‘alaihi wa
sallam.

And the hikmah behind the sending of the Messengers was:

a) to establish the proof. He, the Most High, said:

Messengers as bearers of good tidings and warners in order that mankind
should have no plea against Allaah after the coming of the
Messengers…
Soorah an Nisaa (4) aayah 165

b) as a mercy – as per His statement, He the Most High:

And We did not send you except as a mercy to all
creation.
Soorah al Anbiyaa (21) aayah 207

c) to make clear the path leading to Allaah, the Most High – because
the person does not know what Allaah has made obligatory in a detailed manner
except through the path of the Messengers.

(Al qawl ul mufeed (1/27 to 28) of Shaykh Muhammad ibn Saalih al
‘Uthaymeen rahimahullaah, translated by Nasser ibn Najam)