How did John von Neumann’s work on set theory attract David Hilbert’s attention?

John von Neumann’s work on set theory attracted the attention of David Hilbert primarily through his 1925 paper, "An Axiomatization of Set Theory."1

At the time, Hilbert was a leading figure in the effort to establish axiomatic foundations for all of mathematics. Von Neumann’s earlier 1923 work, "The Introduction of Transfinite Ordinals," had already provided a conventional definition of an ordinal number as the set of all smaller ordinal numbers, which effectively bypassed complications associated with Georg Cantor’s transfinite numbers.1

These contributions aligned with Hilbert’s program, leading to von Neumann’s postdoctoral work under Hilbert at the University of Göttingen from 1926 to 1927.1