Why did Johannes Brahms value a long orchestral introduction in a concerto?

Johannes Brahms valued the long orchestral introduction, or ritornello, in a concerto because he believed it was essential for recovering the depth and grandeur of the concerto form, which he felt had been weakened by composers who followed Felix Mendelssohn in abandoning the practice.1

Brahms viewed the opening orchestral passage as a vital tool for sharpening and deepening the complex relationship between the orchestra and the soloist. By establishing this foundation, the introduction allowed for a more revelatory distribution of themes, keys, instrumentation, and tensions, particularly when the music reached the recapitulation. For Brahms, this structural element was far from superfluous; it was a necessary component for maintaining the taut, dramatic symphonic development that he sought to preserve in his own works.1