Music is a medium which allows for many emotions to modulated upon it. All or most of the ways that a mood changes us, have a corresponding nuance affecting a melody. We can feel loose and free, or tight and apprehensive. We can feel inventive and explorative or hampered and inhibited. There is closeness, loneliness, upbeat, new and fresh, interested, excited, bored, stuck, aloof, above, far away, completely enveloped, under, above, lost, at home, energetic, and generally happy. Music has a parallel for each of these.
It can be so subtle that the composer usually doesn’t plan the theme this way. He tries to engulf himself in a mood and the theme flows forth. The general style is usually planned.
Being that subtle is precisely why it is so powerful. If it were explicit it would not carry emotions; your heart would not read it, and it would be academic. Now that it is not understood it bypasses the brain and is interpreted by the heart who resonates with the nuances.