The phrase "My heart" shows the poet's personal feeling and experience. It reveals that the poet is going to express something dear to him. This reflects the subjective view of the poet personifies his heart as a human being who jumps and springs through the air. This shows the poet's intense joy and happiness at the sight of the rainbow. This scene makes his heart jumps with delight. The word "behold" means "look and think at the same time". The poet looks at the rainbow attentively. He mediates and contemplates on this sight. This sight attracts his attention strongly. He concentrates deeply on this scene. This word refers to the sensory perception.