( أُبَلِّغُكُمْ ) (I convey to you): The Arabic word for (convey) comes from (balagh) which also means what is used to reach the end-goal.

( رِسَالَاتِ رَبِّي ) (the messages of my Lord): The reason why (Messages) was not mentioned in singular is because the Allah (swt) sent many Messages, or because the one true Message combines all the Divine Messages. Allah (swt) says:

 شَرَعَ لَكُم مِّنَ الدِّينِ مَا وَصَّىٰ بِهِ نُوحًا وَالَّذِي أَوْحَيْنَا إِلَيْكَ وَمَا وَصَّيْنَا بِهِ إِبْرَاهِيمَ وَمُوسَىٰ وَعِيسَىٰ ۖ أَنْ أَقِيمُوا الدِّينَ وَلَا تَتَفَرَّقُوا فِيهِ ۚ كَبُرَ عَلَى الْمُشْرِكِينَ مَا تَدْعُوهُمْ إِلَيْهِ ۚ اللَّهُ يَجْتَبِي إِلَيْهِ مَن يَشَاءُ وَيَهْدِي إِلَيْهِ مَن يُنِيبُ

(He has ordained for you of religion what He enjoined upon Noah and that which We have revealed to you, [O Muhammad], and what We enjoined upon Abraham and Moses and Jesus – to establish the religion and not be divided therein. Difficult for those who associate others with Allah is that to which you invite them. Allah chooses for Himself whom He wills and guides to Himself whoever turns back [to Him].) (Ash-Shura: 13)

(the messages of my Lord): Could also mean that in each commandment and prohibition is a Message from Allah (swt) to human beings, and in every information or story mentioned in the Book this honorable Prophet (PBUH) received.

( وَأَنصَحُ لَكُمْ) (and advise you): He was worried about them and gave them advices.

( وَأَعْلَمُ مِنَ اللَّهِ مَا لَا تَعْلَمُونَ) (and I know from Allah what you do not know): He knew more than they did because he was a Messenger informed by Allah (swt), thus he knew what will happen to them and that there would be a flood if they did not respond to his calling. In the verses of Surah Hud, Allah (swt) says:

 وَأُوحِيَ إِلَىٰ نُوحٍ أَنَّهُ لَن يُؤْمِنَ مِن قَوْمِكَ إِلَّا مَن قَدْ آمَنَ فَلَا تَبْتَئِسْ بِمَا كَانُوا يَفْعَلُونَ (36) وَاصْنَعِ الْفُلْكَ بِأَعْيُنِنَا وَوَحْيِنَا وَلَا تُخَاطِبْنِي فِي الَّذِينَ ظَلَمُوا ۚ إِنَّهُم مُّغْرَقُونَ (37) وَيَصْنَعُ الْفُلْكَ وَكُلَّمَا مَرَّ عَلَيْهِ مَلَأٌ مِّن قَوْمِهِ سَخِرُوا مِنْهُ ۚ قَالَ إِن تَسْخَرُوا مِنَّا فَإِنَّا نَسْخَرُ مِنكُمْ كَمَا تَسْخَرُونَ (38) فَسَوْفَ تَعْلَمُونَ مَن يَأْتِيهِ عَذَابٌ يُخْزِيهِ وَيَحِلُّ عَلَيْهِ عَذَابٌ مُّقِيمٌ (39) حَتَّىٰ إِذَا جَاءَ أَمْرُنَا وَفَارَ التَّنُّورُ قُلْنَا احْمِلْ فِيهَا مِن كُلٍّ زَوْجَيْنِ اثْنَيْنِ وَأَهْلَكَ إِلَّا مَن سَبَقَ عَلَيْهِ الْقَوْلُ وَمَنْ آمَنَ ۚ وَمَا آمَنَ مَعَهُ إِلَّا قَلِيلٌ (40) ۞ وَقَالَ ارْكَبُوا فِيهَا بِسْمِ اللَّهِ مَجْرَاهَا وَمُرْسَاهَا ۚ إِنَّ رَبِّي لَغَفُورٌ رَّحِيمٌ (41) وَهِيَ تَجْرِي بِهِمْ فِي مَوْجٍ كَالْجِبَالِ وَنَادَىٰ نُوحٌ ابْنَهُ وَكَانَ فِي مَعْزِلٍ يَا بُنَيَّ ارْكَب مَّعَنَا وَلَا تَكُن مَّعَ الْكَافِرِينَ (42) قَالَ سَآوِي إِلَىٰ جَبَلٍ يَعْصِمُنِي مِنَ الْمَاءِ ۚ قَالَ لَا عَاصِمَ الْيَوْمَ مِنْ أَمْرِ اللَّهِ إِلَّا مَن رَّحِمَ ۚ وَحَالَ بَيْنَهُمَا الْمَوْجُ فَكَانَ مِنَ الْمُغْرَقِينَ (43) وَقِيلَ يَا أَرْضُ ابْلَعِي مَاءَكِ وَيَا سَمَاءُ أَقْلِعِي وَغِيضَ الْمَاءُ وَقُضِيَ الْأَمْرُ وَاسْتَوَتْ عَلَى الْجُودِيِّ ۖ وَقِيلَ بُعْدًا لِّلْقَوْمِ الظَّالِمِينَ (44)

((36) And it was revealed to Noah that, “No one will believe from your people except those who have already believed, so do not be distressed by what they have been doing. (37) And construct the ship under Our observation and Our inspiration and do not address Me concerning those who have wronged; indeed, they are [to be] drowned.” (38) And he constructed the ship, and whenever an assembly of the eminent of his people passed by him, they ridiculed him. He said, “If you ridicule us, then we will ridicule you just as you ridicule. (39) And you are going to know who will get a punishment that will disgrace him [on earth] and upon whom will descend an enduring punishment [in the Hereafter].” (40) [So it was], until when Our command came and the oven overflowed, We said, “Load upon the ship of each [creature] two mates and your family, except those about whom the word has preceded, and [include] whoever has believed.” But none had believed with him, except a few. (41) And [Noah] said, “Embark therein; in the name of Allah is its course and its anchorage. Indeed, my Lord is Forgiving and Merciful.” (42) And it sailed with them through waves like mountains, and Noah called to his son who was apart [from them], “O my son, come aboard with us and be not with the disbelievers.” (43) [But] he said, “I will take refuge on a mountain to protect me from the water.” [Noah] said, “There is no protector today from the decree of Allah, except for whom He gives mercy.” And the waves came between them, and he was among the drowned. (44) And it was said, “O earth, swallow your water, and O sky, withhold [your rain].” And the water subsided, and the matter was accomplished, and the ship came to rest on the [mountain of] Judiyy. And it was said, “Away with the wrongdoing people.”) (Hud)

And in Surah Nooh, Allah (swt) says:

 إِنَّا أَرْسَلْنَا نُوحًا إِلَىٰ قَوْمِهِ أَنْ أَنذِرْ قَوْمَكَ مِن قَبْلِ أَن يَأْتِيَهُمْ عَذَابٌ أَلِيمٌ (1) قَالَ يَا قَوْمِ إِنِّي لَكُمْ نَذِيرٌ مُّبِينٌ (2) أَنِ اعْبُدُوا اللَّهَ وَاتَّقُوهُ وَأَطِيعُونِ (3) يَغْفِرْ لَكُم مِّن ذُنُوبِكُمْ وَيُؤَخِّرْكُمْ إِلَىٰ أَجَلٍ مُّسَمًّى ۚ إِنَّ أَجَلَ اللَّهِ إِذَا جَاءَ لَا يُؤَخَّرُ ۖ لَوْ كُنتُمْ تَعْلَمُونَ (4) قَالَ رَبِّ إِنِّي دَعَوْتُ قَوْمِي لَيْلًا وَنَهَارًا (5) فَلَمْ يَزِدْهُمْ دُعَائِي إِلَّا فِرَارًا (6)

((1) Indeed, We sent Noah to his people, [saying], “Warn your people before there comes to them a painful punishment.” (2) He said, “O my people, indeed I am to you a clear warner (3) [Saying], ‘Worship Allah, fear Him and obey me (4) Allah will forgive you of your sins and delay you for a specified term. Indeed, the time [set by] Allah, when it comes, will not be delayed, if you only knew.’ ” (5) He said, “My Lord, indeed I invited my people [to truth] night and day (6) But my invitation increased them not except in flight.) (Nooh)

Each scene concords with the context in the Surah it was mentioned in.