This passage seems to be a deeply philosophical and spiritual reflection on the potential of human beings. Without any external references, here's how I would understand it, breaking it down line by line:

• "Not for vain repetition were you built;": This suggests that our existence isn't meant to be meaningless or just a cycle of the same things. There's a higher purpose.

• "Out of the Immortal's substance you were made;": This implies a divine origin, that we are fundamentally connected to something eternal and greater than ourselves.

• "Your actions can be swift revealing steps,": Our choices and deeds can quickly lead to profound insights and understanding.

• "Your life a changeful mould for growing gods.": Life is a dynamic process that shapes us, allowing us to evolve towards a more divine or perfected state.

• "A Seer, a strong Creator, is within,": There's an inherent capacity within us for vision, wisdom, and the power to bring things into being.

• "The immaculate Grandeur broods upon your days,": A pure and magnificent presence or power watches over our lives.

• "Almighty powers are shut in Nature's cells.": The very fabric of our being (Nature's cells) holds immense, latent potential.

• "A greater destiny waits you in your front:": Our future holds a more significant and elevated purpose.

• "This transient earthly being if he wills": Our current, temporary human existence has the power, through conscious choice ("if he wills"),

• "Can fit his acts to a transcendent scheme.": to align its actions with a reality that goes beyond the ordinary and material.

• "He who now stares at the world with ignorant eyes": Someone who currently perceives the world without deeper understanding,

• "Hardly from the Inconscient's night aroused,": barely awakened from a state of unconsciousness or unawareness,

• "That look at images and not at Truth,": who focuses on superficial appearances rather than underlying reality,

• "Can fill those orbs with an immortal's sight.": has the potential to gain a divine or eternal perspective.

• "Yet shall the godhead grow within your hearts,": The divine essence will develop and mature within us.

• "You shall awake into the spirit's air": We will awaken to a realm of pure consciousness and spirit.

• "And feel the breaking walls of mortal mind": We will experience the limitations of our ordinary, finite thinking dissolving.

• "And hear the message which left life's heart dumb": We will understand a profound truth that our everyday awareness couldn't grasp.

• "And look through Nature with sun-gazing lids": We will perceive the world with a clear, illuminated, and penetrating vision.

• "And blow your conch-shells at the Eternal's gate.": This evokes a sense of triumph and proclamation at the threshold of the eternal.

• "Authors of earth's high change, to you it is given": We are the agents of significant transformation on Earth, and this ability is inherent to us.

• "To cross the dangerous spaces of the soul": We are meant to navigate the challenging and profound depths of our inner being.

• "And touch the mighty Mother stark awake": To connect with a powerful, fundamental, and fully conscious source of creation or being.

• "And meet the Omnipotent in this house of flesh": To encounter the all-powerful within our own physical existence.

• "And make of life the million-bodied One.": To realize a unity and interconnectedness in all of life, transcending individual limitations.

Essentially, the passage speaks of the immense spiritual potential within humanity, suggesting that we are not merely physical beings but possess a divine core capable of profound transformation, insight, and connection to a higher reality. It emphasizes that through conscious effort and inner awakening, we can move from a state of ignorance to one of divine understanding and become agents of significant change in the world.

Does this initial breakdown help you understand the passage better? Perhaps knowing the author your son refers to might provide further context, but based on the text alone, this is my interpretation.