36-68
And he to whom We give a long life, We reverse him in creation (instead of growing he starts decaying). Do they not then understand?
In old age degeneration and decay start.
36-69
And We have not taught him (Muhammed) poetry and it is not suitable for him, it is nothing but a reminder and a Quran (that makes things) clear,
Muhammed (PBH) has not been taught poetry, it does not suit his office. The Quran is a reminder and a warning for those who are alive to it.
36-71
Did they not see that We have created the cattle for them, among that which Our hands have done, then they are their masters?
Allah (SWT) mentions some of His favours, the benefit we derive from the cattle, we ride some, drink their milk, eat their flesh, use their fur etc. Inspite of this there are some who take other objects for worship who are not capable of helping anyone, including themselves.
36-76
So do not let their speech grieve you, We know that which they keep secret and that which they make public.
Muhammed (PBH) is consoled not to grieve on the speech of the infidels.
36-77
Has not man considered that We created him from a sperm* even then he is an open disputant. [* See note no. 1 of chapter 16, Verse 4]
Man forgets his creation from a microscopic sperm and an egg by Allah (SWT) and disputes against his Creator by doubting His capacity of recreation after his death. Man foolishly questions about his recreation not realizing that the One Who created him for the first time from nothing 19:67 can definitely recreate him from his decomposed bones.