Concerning Allah's statement,
إِذْ تَمْشِي أُخْتُكَ فَتَقُولُ هَلْ أَدُلُّكُمْ عَلَى مَن يَكْفُلُهُ فَرَجَعْنَاكَ إِلَى أُمِّكَ كَيْ تَقَرَّ عَيْنُهَا
When your sister went and said;`Shall I show you one who will nurse him!' So We restored you to your mother, that she might cool her eyes.
When he was accepted into the house of Fir`awn, women were brought in attempts to find someone who might be able to nurse him. But he refused to breast feed from any of them.
Allah, the Exalted, says,
وَحَرَّمْنَا عَلَيْهِ الْمَرَاضِعَ مِن قَبْلُ
And We had already forbidden (other) foster suckling mothers for him. (28;12)
Then, his sister came and said,
هَلْ أَدُلُّكُمْ عَلَى أَهْلِ بَيْتٍ يَكْفُلُونَهُ لَكُمْ وَهُمْ لَهُ نَـصِحُونَ
Shall I direct you to a household who will rear him for you, and look after him in a good manner. (28;12)
She meant, "Shall I guide you to someone who can nurse him for you for a fee."
So she took him and they went with her to his real mother. When her breast was presented to him, he took it and they (Fir`awn's family) were extremely happy for this. Thus, they hired her to nurse him and she achieved great happiness and comfort because of him, in this life and even more so in the Hereafter.
Allah, the Exalted, says here,
فَرَجَعْنَاكَ إِلَى أُمِّكَ كَيْ تَقَرَّ عَيْنُهَا
وَلَا تَحْزَنَ
So We restored you to your mother, that she might cool her eyes and she should not grieve.
This means that she should not grieve over you.
وَقَتَلْتَ نَفْسًا
Then you killed man,
This means that he killed a Coptic person (the people of Egypt, Fir`awn's people).
فَنَجَّيْنَاكَ مِنَ الْغَمِّ
but We saved you from great distress,
This is what he was feeling due to Fir`awn's family intending to kill him. So he fled from them until he came to the water of the people of Madyan.
This is when the righteous man said to him,
لَا تَخَفْ نَجَوْتَ مِنَ الْقَوْمِ الظَّـلِمِينَ
Fear you not. You have escaped from the people who are wrongdoers. (28;25)
Choosing Musa to go to Fir`awn and to be Soft and Gentle in His Invitation
Then Allah says,
وَفَتَنَّاكَ فُتُونًا فَلَبِثْتَ سِنِينَ فِي أَهْلِ مَدْيَنَ ثُمَّ جِيْتَ عَلَى قَدَرٍ يَا مُوسَى
Then you stayed a number of years with the people of Madyan. Then you came here according to the fixed term which I ordained (for you), O Musa!
Allah, the Exalted, says in His address to Musa that he had lived among the people of Madyan, avoiding Fir`awn and his chiefs. He worked as a shepherd for his father-in-law until the appointed time for his work ended. Then he met the decree of Allah and His predetermined will, without him having any set appointment. This entire situation was under the control of Allah, Blessed be He, the Most High. He compels His servants and His creatures to whatever end He wills.
This is why Allah says,
ثُمَّ جِيْتَ عَلَى قَدَرٍ يَا مُوسَى
(Then You came here according to the fixed term which I ordained (for you), O Musa!),
Mujahid said,
"For a set appointment."
Abdur-Razzaq recorded that Ma`mar reported from Qatadah that he said,
ثُمَّ جِيْتَ عَلَى قَدَرٍ يَا مُوسَى
(Then You came here according to the fixed term which I ordained (for you), O Musa!),
"For the decree of Messengership and Prophethood.