The reason why Brahman is beyond human understanding is that human form is but a medium and had no independent standing in cosmic system. It is primarily the spirit existing in our heart, our soul atman that manifested human form to cleanse self of dross impurities within.
The cosmic journey of life truly belongs to our soul atman, consciousness existing in heart. For life to evolve in cosmic system, human beings at times suffered and at other times experienced happiness. Indulging in both, sufferings and happiness, life moved ahead in cosmic life cycle.
Everything relating to Brahman can be understood by indulging in spirituality detailed in Bhagavad Gita and also Upanishads (independent spiritual treatises). Nothing in Bhagavad Gita can be understood literally, prime reason why people world over failed to understand cosmic design.
Indulging in Indian spirituality as contained in Hinduism, we realized that being a spirit, consciousness existing in heart the ultimate goal of life for human beings always remains reaching state of enlightenment, self realization, god realization and finally moksha salvation.
It is during our spiritual sojourn we finally realized meaning of Brahman and its underlying relationship with atman, soul.
For people on earth visualizing, conceptualizing Brahman, God Almighty in English was difficult. In Hinduism religious preachers created many attributes prime of which are Lord Brahma, Lord Vishnu and Lord Shiva. As per Lord Krishna in Bhagavad Gita, none of these attributes ever existed on mother earth. Only to worship Brahman, pray to him religious pundits created these attributes so that masses, commoners can indulge in daily religious routines of life.
All the gods and goddesses existing in Hinduism were only attributes of Brahman, God Almighty.
The real man gods that ever existed on mother earth were enlightened souls like Mahavira, Gautama Buddha, Jesus Christ and Prophet Mohammed. Other than these spiritual stalwarts, hundreds of other enlightened souls existed in the entire history of Hinduism. Adi Shankaracharya, Sri Ramakrishna Paramhansa and Maharshi Ramana are also in the list of enlightened souls who succeeded in reaching God in their lifetime.
Human intellect has its limitations. Almost 98% of human brain lay dormant. Practicing absolute celibacy for a minimum period of 12 years in continuation when seekers indulging in spirituality successfully awakened their kundalini shakti, the coiled Serpentine energy lying dormant in base of spine… did the remaining dormant portion of brain become active. All enlightened ones used their brain 100%. It is at this stage everything about cosmos becomes transparent and clear.
Every enlightened soul can establish a communion with Brahman on one-to-one basis all the time. But for ordinary mortals, commoners even conceptualizing Brahman were difficult.
Hinduism accords Bhagavad Gita the highest privilege that could ever be accorded to a scripture in the spiritual world. Reason being indulging in Bhagavad Gita human beings finally realized what Brahman, atman in reality were all about!