https://www.musical-u.com/learn/tension-release-bitter-sweet-relationships-chords-scales/
How good is that feeling when you finish work at the end of the day? How good is that cold glass of water after working in the sun? That hot shower after swimming in the cold river?
This is all tension and release.
Many melodies consist mostly of chord tones. But when you rely solely on chord tones for your melody, then your melody or improvised line will sound very vanilla or Plain Jane. Not that there is anything wrong with Vanilla and Jane. But music is about Tension and Release. Release is an important aspect of music and life.
Musical-U shares some exercises to explore the next step after learning to hit the chord tones.