Key Themes:

The Dawn as a Divine Entity: The Dawn is personified and addressed as a powerful, benevolent goddess, "Usha Devata," and "lady light of wealth and beauty." (Verse 5) She is described as the "daughter of heavenly light." (Verse 7)
The Relationship between Day and Night: The hymn highlights the cyclical and interdependent nature of Dawn and Night. They are depicted as sisters, "like sisters of the same one brother," (Verse 2) who follow the same "endless and infinite" path in succession, "each retiring and succeeding the other." (Verse 2, 3) They are "of harmonious nature," despite their seemingly contradictory forms of light and darkness. (Verse 3)
The Illuminating and Awakening Power of Dawn: A central theme is the Dawn's ability to dispel darkness and bring light and activity to the world. She is the "light of lights," (Verse 1) "bright and enlightening, rising and expanding." (Verse 1) She "uncover[s] the womb of darkness for the coming of dawn" (Verse 1) and "dispels the darkness of night." (Verse 14) The Dawn "wakes up the worlds of existence into light, beauty and activity." (Verse 5, 6) She is "waking up, inspiring, exciting, even reviving life asleep as dead." (Verse 8)
The Dawn's Benefits and Blessings: The hymn enumerates the positive effects of the Dawn. She brings "inspiration and revelation of divinity for spirits of piety" (Verse 4) and "opens the doors of intelligence and consciousness." (Verse 4) She "reveals the wealth of nature and envelops the worlds of existence in beauty and splendour." (Verse 4) The Dawn is beneficial for a wide range of beings and activities, from the lazy and weak-eyed to those seeking "enjoyment of living," "attainment of desire," "achievement of wealth," (Verse 5) "governance and administration of the social order," "food, energy and national prestige," "honour and grandeur," and "reaching the desired goal in life." (Verse 6) She is a "harbinger of peace and comfort," a "messenger of felicity," bearing "joy and prosperity fit for divinity." (Verse 12)
The Eternal and Recurrent Nature of Dawn: The hymn emphasizes the timeless quality of the Dawn. She "follows the path of those that have gone before since eternity" and is the "first pioneer of those that would follow for eternity." (Verse 8) The Dawn is described as "ancient and eternal" and "unaging and immortal." (Verse 13) Mortals may pass away, but the Dawn continues, linking generations through the "light of life." (Verse 11)
The Dawn as a Catalyst for Human Action and Devotion: The Dawn is linked to human activities, particularly yajna (sacrifice) and devotion. She facilitates the "lighting of the fire of yajna early morning" (Verse 9) and "awake[s] and inspire[s] the devotees of yajna." (Verse 9) The hymn encourages the worshipper to seek the Dawn's light, health, and progeny. (Verse 17) The Dawn is generous "for the man who gives and sacrifices." (Verse 18)
The Dawn and the Cosmic Order: The hymn places the Dawn within a larger cosmic framework. She is connected to the sun ("bearing the bright sun new born," Verse 2; "cleared the path for the sun to rise and move," Verse 16) and is seen as a force that contributes to the order of the universe ("as ordained by the Divine," Verse 3). The final verse invokes various cosmic entities – Mitra, Varuna, Aditi, the rivers, the sea, the earth, the sky, and the light of heaven – to expand and elevate the benefits brought by the Dawn. (Verse 20)

Most Important Ideas/Facts:

The personification of Dawn (Usha) as a powerful and benevolent goddess is a fundamental concept in this hymn.
The cyclical relationship between Dawn and Night, depicted as harmonious sisters, is crucial to understanding the Vedic worldview of natural cycles.
The transformative power of Dawn to dispel darkness and bring light and activity is a central message, emphasizing its vital role in life and the cosmos.