As for the Prophet's saying: "raghbatan wa rahbatan ilaika," it means: all the supplications I said were out of my desire and fear. Willing fully for Your Ample Favor and Great Bounty and fearing of You and of everything that incurs Your Wrath. This is the usual condition of prophets and pious people from the servants of Allah who always combine between desire and fear. As Allah (may He be Exalted) says: "So We answered his call, and We bestowed upon him Yahyâ (John), and cured his wife (to bear a child) for him. Verily, they used to hasten on to do good deeds, and they used to call on Us with hope and fear, and used to humble themselves before Us." [Surat Al Anbiya': 90]. Then the Prophet (peace be upon him) said in this invocation: "la malja'a wa la manja minka illa ilaika" which means: There is no shelter, escape, or rescuer from Your Punishment except by resorting to You in fear and reliance as Allah (may He be Exalted) says: "So flee to Allâh (from His Torment to His Mercy - Islâmic Monotheism)." [Surat Adh-Dhariyat: 50]. Allah (may He be Exalted) also says: "No! There is no refuge! * To your Lord (Alone) will be the place of rest that Day." [Surat Al Qiyamah: 11 - 12]. Then he says: "Amantu bikitabikal-ladhy anzalta wa bi nabiyyikal-ladhy arsalta'" which means: I have believed in Your Glorious Book (The Glorious Qur'an) which falsehood cannot come to it from before it or behind it: (it is) sent down by the All-Wise and the Worthy of all praise (Allah Exalted and Sublime). I have believed and admitted that the Glorious Qur'an is Your revelation that was sent down to Your Servant and Messenger, our Prophet Muhammad (peace be upon him), and we believe that it contains the truth, guidance and light. I have also believed in Your Prophet whom You sent i.e., Muhammad (peace be upon him), the servant, Messenger, and the best of people who was sent as a mercy for all the worlds. I have believed in what he came with because he (peace be upon him) does not utter out of desire or whim, but he is a revelation revealed, so all that he came with is the right and truth.
As for the Prophet's saying: "al-ladhy arsalta," it means: to all creatures as a bringer of glad tidings, a warner, and a caller to Allah by His Leave and a luminous lamp. He truly delivered the message, rendered the trust, advised the nation, and fought in the way of Allah truly until he passed away.
Then the Prophet (peace be upon him) said, showing the virtue of this invocation and the great reward and favor gained from this supplication: "If you should die then (after reciting this) you will die on the religion of Islam (i.e., as a Muslim)" As Allah (may He be Exalted) says: "So set you (O Muhammad peace be upon him) your face towards the religion (of pure Islâmic Monotheism) Hanîf (worship none but Allâh Alone). Allâh's Fitrah (i.e. Allâh's Islâmic Monotheism) with which He has created mankind. No change let there be in Khalq-illâh (i.e. the religion of Allâh - Islâmic Monotheism)." [Surat Al `Ankabut: 30]. It was reported in some of the narrations of this Hadith that he said: "And if you get up in the morning you would get up with a bliss." which means: If you do not pass away this night, the next morning you shall gain goodness as a reward for you for your concern with this matter. The Prophet (peace be upon him) instructed Muslims to make this invocation from the last supplications a Muslims says before going to sleep; therefore, he said: "Made them the last of your invocations."
As in Prophet's saying to Al Bara' when he repeated the invocation before him so that he would memorize it: "No, and in Your Prophet whom You revealed to." a proof to the importance of pronouncing these Adhkar (invocations and Remembrances said at certain times on a regular basis) with their exact wordings because of their perfection in semantics and meanings.
This is a great invocation which a Muslim should keep to before going to sleep and ponder over its implications and great meanings in order to win the promised reward. I supplicate Allah the Ever-Generous to guide you and us to keep to these invocations and guide us to all good that He loves and satisfies in this world and in the Hereafter.