If the text in the excel spreadsheet is in a particular cell, you can identify this and insert this into a text box in ArcMap. You need to name the element in ArcMap so this can be referenced later on.
Please read the link for more information.
import xlrd
import arcpy
wb = xlrd.open_workbook("YOUR_FILE.xls") # xls file to read from
sh1 = wb.sheet_by_index(0) # first sheet in workbook
# rowx and colx (x for Excel) start at 1!
excelttext = sh1.cell(rowx=3,colx=2).value
mxd = arcpy.mapping.MapDocument(r"C:\Project\Project.mxd") #insert MXD
for elm in arcpy.mapping.ListLayoutElements(mxd, "TEXT_ELEMENT", "NAME_OF_ELEMENT"): # insert text element name
elm.text = exceltext
arcpy.RefreshActiveView()
mxd.save()