Brahman is the central theme of Sanatan Dharma. Brahman is the indescribable, inexhaustible, omniscient, omnipresent, original, first, eternal and absolute principle who is without a beginning, without an end , who is hidden in all and who is the cause, source, material and effect of all creation known, unknown and yet to happen in the entire universe.
At further lower level there exists a trinity concept. The trinity concept of Hindus is different from that of other religions. Here the ‘controllers’ of birth, existence / growth and death are symbolically presented in human forms as Brahma Vishnu Maheswara – trimoorthy sankalpa in which the universal laws of life cycle are symbolically presented . Mahavishnu is the base for the trinity concept.
Explanation for Mahavishnu: The blue colour of Vishnu denotes the colour of the sky and ocean which means the infinity/ limitless. The serpent on which Vishnu is lying denotes the coiled structure of galaxy. The name of the serpent anantha means limitless (infinity) the ksheera saagaram ( ocean of milk) on which Vishnu is pictured shows milky way galaxy. Anantha sayana represent the silent universe/ galaxies. Symbolically Mahalakshmi ( meaning of this word is prosperity) has been attributed the position of the wife of Mahavishnu showing that any system can smoothly exist only with prosperity.
From Mahavishnu comes out through a Lotus (symbolically) the creator Lord Brahma. This symbolically presents a connection of Lord Brahma with the prapancha purhsa similar to the connection of the baby in the womb of the mother. The baby takes the energy and nutrition for growing/ cell production from the mother. Similarly Lord Brahma takes energy and material from for creation in the world. The four heads of Lord Brahma represent the four axes required for any creation: x, y, z and time axes. The Vedas (the word itself means knowledge) in the hands of Lord Brahma and the position of Saraswathy (deity of knowledge) as the wife of the creator symbolically present that for every creation knowledge/ vidya is required. The knowledge and creation (knowledge for creation) are inseparable components.
Lord Siva is the deity symbolically presents the controller of death/ destruction (the destruction is for further construction). Mahavishnu and Lord Siva are said to be connected through hearts (which only means inseparable)
Vishnoasya hrudayam siva: Sivosya hrudayam vishno – says Upanishads and Yajurveda.
Symbolically Lord Siva has powerful fire in the third eye, powerful water and torrential air symbolically tied in the tuft and the snake around the neck (symbol of international medical association) and thri sool in hand. All the five respectively present destruction through fire, water (flood , etc) air ( cyclone/ tempest, etc) diseases and using weapons. Parvathy (means energy/force/sakti) is symbolically presented as the wife of Lord Siva . Through this combination of Lord Siva and Parvathy, it is shown that the destruction for construction can take place with powerful application of any one or more of the above five. (powerful fire, air, water, diseases and weapon only have the destruction capacity).
Thus they become inseparable hence the concept of Ardhanaareeswara comes up. In fact the Brahma Vishnu Maheswara sankalpa and the Lakshmi Parvathy Sarswathi sankalpa are the symbolic presentation of the life cycle at spiritual‐ social and physical level when scientifically explained. Always the Hindus consider the knowledge, prosperity and sakthi/power in feminine gender.
1. In the Physical plane, that is within ourselves, Brahma resides as the psychic element, Vishnu as the mental element and Siva as the physical element. In other words, Brahma is the intuitive mind, Vishnu is the conscious mind and Shiva is the physical body.
2. In the mental plane, Brahma manifests as creative ideas, Vishnu as the inspiration and Siva as the doubt and hesitation. Brahma manifests as the thought, Vishnu as the action and Siva as the corrective action. In us Brahma is the initiator, Vishnu the perpetuator and Siva the remover. Inside the mind, Brahma manifests as thoughts, Vishnu as positive feelings and emotions and Siva as the negative ones.
3. In the earthly plane, Brahma is the sky, Vishnu is the Sun and Siva is the moon. Among the regions, Brahma is the upper region, Vishnu the middle region and Siva the lower region. In a day, Brahma is morning, Vishnu is afternoon and Siva the night. Among directions, Brahma is east, Siva is west and Vishnu is all that is in between.
4. In Nature they manifest as the three qualities or gunas, which are described in the Bhagavadgita, namely sattva (purity), rajas (egoism) and tamas (darkness). According to the original Vedic tradition, Brahma represents sattva, Vishnu represents rajas and Siva represents tamas. According to the Vaishnava tradition, which presently dominates the mainstream popular Hinduism, Brahma represents rajas, Vishnu represents sattva and Siva represents tamas.
5. Among the paths of salvation, Brahma manifests as the path of knowledge, Vishnu as the path of action and devotion and Siva as the path of renunciation.
These explanations (of the gods) are the connecting layers of Vedic concepts of Brambhan.
Further going at common mans level, the above six deities can be seen in different roles of puranic stories to convey the message of what they represent symbolically in. However these stories are mainly for conveying the values and universal truths in our life. And they are meant for the understanding for less educated common man who may not be in a position to understand the Brahman or prapancha purusha concept, or the symbolic message of Hindu trinity concept, etc.