If the heading for Chapters 1.2 & 1.3 use Heading Styles, you might try something based on:
Selection.GoTo What:=wdGoToBookmark, Name:="\HeadingLevel"

This will expand the selection to include the heading that contains the insertion point or selection, plus any subordinate headings and text. If the current selection is body text, the "\HeadingLevel" bookmark includes the preceding heading, plus any headings and text subordinate to that heading.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]