Understanding the Term 'Ardor' in Context

In the historical accounts of the renowned artist, it is noted that a certain ardor consumed him as he immersed himself in his craft. His brushstrokes were an epitome of fervor, each stroke a declaration of his passion, yet within his art, a subtle melancholy lingered. Critics often proclaimed that while his works radiated brilliance, they also bore an undercurrent of poignant yearning. This complex interplay of emotions left viewers spellbound, inciting both admiration and contemplation.

In this context, the word 'ardor' is central to understanding the artist's devotion. How would one define 'ardor' based solely on this passage?