“does anything.” The context is sin. The person who sins any sin.
“defiantly.” The Hebrew uses an idiom: “with a high hand,” meaning defiantly, deliberately, “a conscious and willed transgression of the law” (cp. BDAG Heb.-English lexicon). There were sin offerings for unintentional sin (Lev. 4:2, 13-14, 22, 27; Num. 15:22-29), but if a person knew the commands of God and simply defied them and showed contempt for them, there was no sin offering for them (Num. 15:30-31). That fact is then emphasized in the text by the example of a man who gathers wood on the Sabbath rather than keeping it holy and not working on the Sabbath, and that man was cut off from the congregation and killed (Num. 15:32-36).
The limitations of the sin offering in the Mosaic Law serve to point out that Jesus Christ was a much more complete sin offering than the sin offerings described in the Law. When Jesus came it became clear that his death would atone for both intentional and unintentional sin. The person who humbly confesses sin is forgiven of all sin and unrighteousness (1 John 1:9). Christ was the sin offering who died in place of sinners and because of his sacrifice believers are declared righteous in the sight of God (Rom. 5:6-11).
“soul.” In this context, “soul” means an individual person. [See Appendix 7, “Usages of ‘Soul’”].