You can use NATURAL JOIN
select * from foo natural join bar
Works as long as the keys are named the same. However, a lot of people have a habit of naming keys differently in the two tables.
A foreign key is effectively a reference to another column, but to de-reference it you have to tell the database which table and column it's a reference to. Every time. Even when this information is already specified in a foreign key constraint.
The author is talking about (not) being able to specify the "from" table and column without having specify the "to" table and column (i.e. tell the database how to de-reference it) on each query. A natural join removes the need to specify the columns, but still requires specifying both tables. So besides requiring a de facto single namespace for columns across tables and generally seeming like a footgun, it doesn't achieve the same thing.
This makes naming key columns differently a defence technique, so you stop people from using natural joins.
select * from foo join bar on (foo.x = bar.y) if the columns have a different name.
I tend to write my joins first, then use where clauses as filters. A select * from foo left inner join on (foo.x = bar.y) is semantically equivalent to foo, bar where foo.x = bar.y, but keeping the joins separate from the filters makes the query more clear.