There are two selves, the separate ego and the indivisible Atman. When one rises above I and me and mine, the Atman is revealed as one’s true Self.
(Katha Up. Part 2, 3:13, p. 97)

“Self” is the innermost Soul in every creature, which is divine.
(Upanishads, p. 305)

God-within-the-creature is known in the Sanskrit language as the Atman or Purusha, the authentic Self… According to the Upanishads and the Gita, the one Atman is present within all creatures.

The Self

Bright but hidden, the Self dwells in the heart.
Everything that moves, breathes, opens, and closes
Lives in the Self. Self is the source of love.
And may be known through love but not through thought.
Self is the goal of life. Attain this goal!
(Mundaka Up. Part 2, 2:1, p. 113)

The aspirant who is seeking the Lord must free himself from selfish attachments to people, money, and possessions. When his mind sheds every selfish desire, he becomes free from the duality of pleasure and pain and rules his senses. No more is he capable of ill will; no more is he subject to elation, for his senses, come to rest in the Self.
(Paramahamsa Up. 4, p. 246)