Wathkur fee alkitabi moosa innahu kana mukhlasan wakana rasoolan nabiyya (surah Maryam: 51)

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(19:51) And mention in this Book Moses: he was a chosen person," *29 and he was a Messenger Prophet. *30

Wazkur fil Kitaabi Moosaaa; innahoo kaana mukhlasanw wa kaana Rasoolan Nabiyyaa

*29) The word used is mukhlas, which means "purified". In other words, Allah had specially chosen Prophet Moses for the Mission of Prophethood.
*30) "Rasul" literally means `the one who is sent'; therefore it is used for an ambassador, envoy, messenger and representative. The Qur'an has used this title for angels, who are sent by Allah on a special mission, or for the human beings who brought His Message to mankind.
As regards the word "Nabi", it literally means the one who brings news, or the one who is high in rank, or the one who shows the way. This title is used for the Prophets in all the three senses. Thus Moses was a Messenger Prophet because he was a Messenger of high rank who gave news from Allah and showed the Right Way to the people.
The Qur'an does not necessarily differentiate between the use of the two titles, for sometimes it uses the title Rasul for one person at one place and the title Nabi for the same person at another place, and sometimes uses both the titles together for one and the same person. However, at some places each title has been used in a way as to show that there is some technical distinction between the two, though that has not been precisely marked out, except that every Rasul (Messenger) is a Nabi (Prophet) as well, but every Nabi may not be a Rasul, and that a Rasul has a special and more important mission to perform. This is supported by a Tradition of the Holy Prophet, which has been reported by Imam Ahmad from Abu Umamah and by Hakim from Hadrat Abu Zarr. When the Holy Prophet was asked how many "Messengers" and "Prophets" had been sent to the world, he said that the number of the Messengers was 313 or 315 and of the Prophets 1,24,000