P is inside the quotes, so it is just "p".

You need it outside the quotes

ActiveCell.Rows("1:" & p).EntireRow.Select

the logic of the syntax eludes me--I guess it's just
something I'll have to memorize . . .and remember . . .

In some computer programming languages it is possible to
place variable names inside quotes and have the language
interpreter interpolate the value. Perl scalar variables, for
example start with a "$".

This prints "1:220" (without the quotes) in Perl.

my $p = 220;
print "1:$p";


In VBA, variable names do not have a sigil (like $ or @)
in front of them. It is more difficult to interpolate variables
inside quotes when variable names look like common words. The
VBA language writers decided that they would avoid confusion
by not interpolating variable names.

If they had not decided this, we would have problems
printing this.

Dim p as Integer
p = 220
Debug.Print " Have a Happy Day!"

With interpolation this would print the following in the
immediate window.

Your syntax "1:p" was a quoted string with three characters in it: a
numerical 1, a colon, and a lower-case "p".

My syntax "1:" & p is a string concatenation operation that will concatenate
"1:" with the contents of the variable p.

Do some string operations in normal code and you'll become familiar with the
syntax.