The strongest signs:
The creation of man is indeed a sign for those who think and take lessons.
{And in yours elves. Then will you not see?}
[Surat adh - Dhāriyāt: 21]
Within human beings themselves, there are the greatest signs of their Almighty Creator.
The closest thing to a person is his own self. In fact, he contains wonders that point to the greatness of Allah Almighty that would take our whole life just to discover part of it. People turn away from this, however, and if they only pondered, they would cease to deny or disbelieve.
{Cursed is man; how disbelieving is he!From what substance did He create him? From a sperm - drop He created him and proportioned him;Then He eased the way for him;Then He causes him to die and puts him in his grave.Then when He wills, He will resurrect him.}
[Surat ‘Abasa: 17-22]
Over 7 billion people live on earth. Each one of them has his or her different form, shape, features, color, and appearance, though they all come from the same father and mother: Adam and Eve. But it is the work of Allah Almighty:
{...[It is] the work of Allah, Who perfected all things. Indeed, He is All -Aware of what you do.}
[Surat an-Naml:88]
Does this not require us to be thankful?! We see the favors that Allah Almighty bestows upon us since we were mere drops of sperm inside our mothers’ wombs. Then, He gave us hearing and eyesight and breathed life into us. Then, He gave us food and drink and endowed us with homes and provisions, and everything we need.
{Have We not made for him two eyes? And a tongue and two lips?And have shown him the two ways?}
[Surat al - Balad: 8-10]
One of the greatest ways in which we can show gratitude to our Lord is to use His blessings in worshiping and obeying Him, not in sins and things displeasing to Him.