Signs (Aayaat plural of Aayah) are that which indicate something and make it clear. Then the signs of Allah, the Most High, are of two types: signs in creation, and signs in His Revealed way (Sharee’ah).
The signs in creation are those things which He created, and the signs in His Revealed way are what is found in His Revelation, which Allah sent down to His messengers. So the saying of the author, rahimahullaah,‘through His signs and those things which He has created‘ is an example of mentioning something particular after that which is general. So therefore, the aayaat are divided into three categories:
al-Aayaatul-Burhaaniyyah (evidential signs):
These are the miracles that occurred at the hands of the Messengers and Prophets, such as the miracles that occurred at the hand of Moosaa (’alayhis-salaam) including the clear aayaat. From them is the splitting of the sea, from them is the sticks, from them is the blood, the frogs, lice and locusts which Allah the Mighty and Majestic informed about in Sooratul-A’raaf; all of them are miracles.
And reviving the dead by the permission of Allah are also miracles, and whatever emanated from our Prophet Muhammad (sallallaahu ’alayhi wa sallam) from the numerous miracles, such as the splitting of the moon, the glorification by the pebbles in front of him, the water gushing forth, the submission of the two trees to him, the rock sending salutations upon him and other than that from whatever has been confirmed from the Prophet (sallallaahu ’alayhi wa sallam) from the miracles.
al-Aayaatul-Sharee’ah (Qur’aanic signs):
These are whatever Allaah the Blessed and Exalted sent down upon His Messengers from His speech, from that is the Torah, the Bible, the Psalms, the Furqaan (Qur‘aan) and the scriptures of Ibraaheem and Moosaa and other than that from what Allah has left from His knowledge. All of this enters into the phrase ‘His aayaat.’
al-Aayaatul-Kawniyyah (universal signs):
That is, then say, ‘By His universal signs.’ Therefore, observing the universe proves the greatness of this creation. So it is not possible that this universe came into being all of a sudden, nor is it possible that it was produced by something from the created beings, nor it is possible that the creation created itself. All of that is self-delusion. Therefore, the only possibility which remains is that universe which is witnessed and which is from the great aayaat is an evidence for the existence of al-Khaaliq (the Creator) the Glorified and Exalted. And the Creator is Allah alone.
And the meaning of that is this world with its heavens, its earth and whatever is in between them. All of these are from Allah’s signs which prove His complete and perfect Power, and complete and perfect wisdom. So the sun is one of Allah’s signs, in its wonderful and well-ordered course which it has followed since Allah, the Mighty and Majestic, created it, and which it will follow until Allah, the Most High, grants that the universe is destroyed. So this is its appointed course, as Allah, the Most High, says,
“And the sun proceeds upon its fixed course, (for a term appointed) that is the decree of the All-Mighty, the All Wise.”
[Soorah Yaa Seen (36):38]
Its size and its effects are from the signs of Allah. As for its size, then it is tremendously great; and as for its effects, then it produces benefit for our bodies, for the trees, the rivers, the oceans and other things besides. So if we consider the sun,this great sign, and the great distance that there is between us and it, yet despite this we feel its great heat. Then consider the light it produces which saves the people huge amounts of wealth in the daylight hours when they have no need of other sources of light, so it is indeed a very great sign, and most people perceive only very few of the signs. Likewise the moon is also from the signs of Allah, the Mighty and Majestic, and He decreed for it measured stations.  Each night it has its particular station,
“We have prescribed measured phases for the moon till it returns like an old withered palm-stalk.”
[Soorah Yaa Seen (36):39]
So whichever the case then knowledge of Allah, the Mighty and Majestic, is arrived at through His signs in the creation, the tremendous things contained therein which are wondrous creations and clear proofs of perfect wisdom; and likewise through the signs in His Revealed way, and the justice to be seen in it and how it comprises all that is beneficial and repels all that is corrupt. ‘And in everything there is a sign for Him, Proving that He is One.’
 Extracted from Saaluf- Us- Saalih.com with some modifications
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