The transcriptional regulation of the genome is controlled primarily at the preinitiation stage by binding of the core transcriptional machinery proteins (namely, RNA polymerase, transcription factors, and activators and repressors) to the core promoter sequence on the coding region of the DNA. However, DNA is tightly packaged in the nucleus with the help of packaging proteins, chiefly histone proteins to form repeating units of nucleosomes which further bundle together to form condensed chromatin structure.  Such condensed structure occludes many DNA regulatory regions, not allowing them to interact with transcriptional machinery proteins and regulate gene expression. To overcome this issue and allow dynamic access to condensed DNA, a process known as chromatin remodeling alters nucleosome architecture to expose or hide regions of DNA for transcriptional regulation.
By definition, chromatin remodeling is the enzyme-assisted process to facilitate access of nucleosomal DNA by remodeling the structure, composition and positioning of nucleosomes.