"This kind of prelude was succeeded by the concerto itself which he executed with a degree of spirit and firmness that no one has ever pretended to equal"

This quote is referring to an efficiency of a concerto by an artist. John Hawkins is commending the musician's efficiency, keeping in mind that it was full of spirit and suppleness. He is suggesting that the musician's efficiency was so great that no person has actually ever before been able to match it. This recommends that the musician was exceptionally gifted and that their efficiency was of a really high requirement. It is most likely that the musician was able to capture the emotion of the piece and share it to the target market in a powerful means. The quote is a testament to the musician's skill as well as talent, and it is clear that John Hawkins was very amazed by the performance.