I think the replies that focus on the inner state of mind are spot on.
I’m surprised no one has mentioned the lemniscate (the infinity symbol). Waite saw it as a representation of the Holy Spirit, which brings a Christianized element to this card.
Strength, or Fortitude, involves overcoming a challenge—whether physical or metaphysical—through perseverance. Waite’s definition includes qualities like power, energy, and courage, all linked to this classical virtue. These traits help us face any threat.
The Roman Catholic Church embraced the four classical virtues (Strength, Justice, Prudence, Temperance) and added three theological virtues (Faith, Hope, Charity), making seven virtues around 500 A.D. Early tarot decks reflected these, and some, like the Florentine Minchiate, included all seven.
Fortitude, a gift of the Holy Spirit, is often linked with Christian martyrs—those who faced lions in the Roman Colosseum. The story of Androcles and the Lion fits here: Androcles saved a lion, and later, the lion spared him in the arena. They walked together, joined by a bond similar to the garland of flowers connecting the woman and lion in the Strength card.
Whether the lion’s mouth is open or closed doesn’t matter—it’s clear that there’s love and trust between them, just like with Androcles’ lion.
Waite’s mystical Christianity had a big influence on how he crafted the Major Arcana, and this card is no exception.