Durgaa Sapt Shatee, aka Devee Mahaatmya (called in Southern India) or
Chandee Sapt Shatee or Chandee Paath (in Eastern India), or
Devee Bhaagvat (in Western India) is a collection of 700 verses about Divine Mother. It is from Maarkandeya Puraan.

These 700 verses are arranged in 13 chapters. Also, they are arranged in 3 parts (Charitra). Some parts have more chapters and some parts have fewer. The three parts have Mahaaa Kaalee, Mahaa Lakshmee and Mahaa Saraswatee as the deities. They have Rig Ved, Yajur Ved and Saam Ved as the Swaroop, i.e. each Ved is a different representation/form/essence of each part. The purpose of these three parts are Dharm, Arth and Kaam respectively. They have Aim, Hreem and Kleem as the Beej. Some people mistakenly think that it is merely an account of the exploits of Durgaa and her slaying of demons Mahish, Chand, Mund, Raktabeej, Shumbh, Nishumbh etc but it is not so. They view it as a collection of stories. But that is a very narrow view of the Durgaa Sapt Shatee. Devee Mahaatmya is much more than a collection of stories. Ved are its Swaroop

Devee Mahaatmya is the very definition of the nature of Divine Mother. When it is said Divine Mother, it does not mean limited forms. I am talking about unlimited Shakti (energy) behind all limited Shakti to whom some people call Durgaa, some call her Chandee and some call her Mahaa Lakshmee. The name does not matter that much. Bottom line is that She is the Mool Prakriti, the root nature, of all that manifests. She is the force that drives everything in the universe.

Towards the end, the 11th chapter (titled "Naaraayanee Stuti") describes gods praying to the Divine Mother after slaying all the demons. They address her as "Naaraayanee". This is consistent with the difference between Naaraayan and Vishnu. Vishnu is one of the Tri-Moorti. He is of Sattwa Gun and sustains the creation. Naaraayan is Gunaateet (above Gun / attributes). He is the Sahastraasheersh and Param Purush. Some people may describe the same as Shambhu Sadaa Shiv, but let us not get caught in names. When we are essentially speaking about an entity that is beyond attributes, it is foolish to argue about the name. After all, name too is an attribute. Though great people gave different names to the Param Purush, the names essentially capture the nature of the path those people took to experience the Param Purush rather than the nature of Param Purush, which is beyond names and attributes.

The bottom line is that there is a Param Purush above the Tri-Muoorti (Brahmaa, Vishnu and Shiv). If we call him Naaraayan, then Naaraayanee is his Shakti and She is the root cause of all creation. She is inseparable from Him. Don't imagine Naaraayanee as a separate form. That is a mistake. She is simply the power of Naaraayan. Neither Naaraayan nor Naaraayan have a form. After all, Naaraayan is Gunaateet and formless. Though He CAN take forms, but forms only "limit" Him. His highest nature is that He has no form or attributes. Similarly, Ambaa is not a separate person, but simply the power of Shambhu Shiv. They are inseparable.

These nine Shakti who fought with demons, i.e. Brahmaanee, Maaheshwaree, Kaumaaree, Vaishnavee / Lakshmee, Vaaraahee, Naarasinhee, Shivadootee and Chaamundaa / Kaalee, are all described as different forms of Naaraayanee. Thus, Devee Mahaatmya is essentially about the Shakti of Gunaateet Param Purush (Naaraayan). All Devtaa come from Him and hence the Shakti (energies) of all Devtaa come from His Shakti (Naaraayanee). Thus, Devee Mahaatmya is about the nature of the most supreme energy of this universe! Though Devee Mahaatmya looks like stories, there are very valuable lessons on her nature in it. The deeper you go, the more you can understand and appreciate the lessons in the stories. Let us take a couple of examples.

(1) When various Mothers are going to war with demons, this is how it is described (8-14) : "Whatever form, decoration, weapons and vehicle each god has, his Shakti (energy) came in the same form, decoration, weapons and vehicle." The next 9 verses describe how Brahmaanee etc came. For example, Brahmaanee came on a swan with Aksh Sootra and Kamandal (borne by Brahmaa), Maaheshwaree came on a great bull with a Trishool and she wore a big snake and Moon. And so on. What is the message hidden in the above description? The fact that these female deities are identical to the male counterparts in form, decoration, weapons and vehicles suggest, that they are not really separate from the male counterparts. Brahmaa and Brahmaanee are not separate. Maheshwar and Maaheshwaree are not separate. Vishnu and Vaishnavee are not separate. And so on. Brahmaanee is simply the Shakti (vitality/energy) of Brahmaa. Maaheshwaree is simply the Shakti (vitality/energy) of Maheshwar. And so on.

(2) Take the example of Raktbeej's slaying. Raktbeej is a demon with a special ability. If a drop of his blood falls from his body on the ground, another demon will be born from it and will be of the same size, age and strength as the original Raktbeej even at birth. As Vaishnavee, Maaheshwaree, Aindree etc were hurting Raktbeej in the fight, more and more demons were being born and all the gods were scared. Then Chandikaa told Kaalee to expand her face and eat all the demons as they are born. Chandikaa goes around the battlefield eating all the demons as they are born and eventually Raktbeej also runs out of blood.

This looks a nice story. But, there is a deeper meaning in it. Why was Kaalee the chosen one, and not Vaishnavee or Naarasinhee or Aindree? The word Rakt means blood. Another meaning of Rakt is "desire/passion". Actually, both the meanings are linked and the word comes from the root Ranj / Rang, which means "to color". Of course, in our astrology also, Moon shows Rakt Dhaatu (blood) and he is also the Kaarak for desires. Raktbeej means "the seed of desire". Raktbeej fighting with gods symbolizes desires taking the better of our good judgment and good qualities. Each human being is a microcosm of the macrocosm that the universe is. All Devtaa reside in us as various good qualities and all demons reside in us as various undesirable qualities. When we are overcome by desires and do bad deeds, the Raktbeej within us is defeating the gods within us.

Then why Kaalee was chosen to destroy him? In astrology, we associate Mahaa kaal and Mahaa Kaalee with Saturn. Kaalee shows detachment and Vairaagya. She wears a garland of skulls, symbolizing that there is an endless cycle (garland) of births a material form (skull) goes thru. The way Kaali shows to overcome the cycle is Vairaagya and detachment. She shows meaningful and highest level of Vairaagya that comes with a deep understanding of the cycle of material forms. To fully cut off the "seed of desires", so that one does not get any more desires, one needs to develop Vairaagya and detachment and keep on destroying desires as they are born and persist like that. After persisting for a long time, the "seed of desires" will run out of desires and one will overcome desires.

Thus, simple stories have deep meanings. This particular story celebrates the value of detachment, Vairaagya and persistence - Saturnine qualities. Durgaa Sapt Shatee is what is used in Chandee homam. It is very auspicious to read every day or on Ashtamee or Navamee or Chaturdashee days. It takes 1 to 2.5 hours. If you don't have much time, you may want to read one chapter per day. Merely chanting it without understanding the meaning is also excellent and produces results. Understanding the meaning and marveling at the power of the Mother makes one fearless and energetic and also give material benefits. Understanding the deeper meanings and appreciating the true nature of the Mother makes one realize one's own true nature. It has various benefits at various levels of Saadhanaa. It is tough to exactly say what benefit it gives, as that depends on the evolution level of Saadhak and his attitude. But, there is something in Chandee Paath for everyone! It is more effective if you read the Mool Mantra (the Navaaksharee Mantra or, preferably, Dashaaksharee Mantra with Om added) 108 times before AND after chanting 700 verses.

Although there are no classical references, to my knowledge, on the mapping between the nine planets and the nine forms of Naaraayanee described in Sapt Shatee, who fought with demons, but obviously there must be some kind of link. Here is my first shot at it:
Brahmaanee : Jupiter
Maaheshwaree : Moon
Kaumaaree : Mars
Vaishnavee : Mercury
Vaaraahee : Rahu
Naarasinhee : Ketu
Aindree : Sun
Shivadootee : Venus
Chaamundaa or Kaali : Saturn

Reading the meaning of Chandee Paath is also good and creates positive thoughts. But repeating the Sanskrit Mantra (even without understanding the meaning) is superior to that! It creates well-understood energy in the consciousness. If one carrying a seed does not understand what it is for and makes a replica in gold, which in his opinion is better, he is losing the basic functionality of the seed. The golden seed may appeal to one as it does not get spoilt and looks better to one's senses, but it can never give rise to a plant. The original seed, on the other hand, can give rise to a plant even when he does not know whose seed it is.