NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index

Can anyone tell me why postgres is creating a implicit index when
I already have a PKEY specified????

Or am I just interpreting this all wrong?

Here is the entry I am putting in:

create sequence journal_line_id_seq increment 1 start 1;

create table journal_lines ( journal_line_id int4 PRIMARY KEY DEFAULT NEXTVAL('journal_line_id_seq'), entry_id int4,
account_idint4, line_type int2 CHECK (line_type >= 1 AND line_type <= 2), line_amount money, CONSTRAINT eid FOREIGN
KEY(entry_id)REFERENCES journal(entry_id), CONSTRAINT aid FOREIGN KEY(account_id) REFERENCES accounts(account_id)
 
);

Here is the notice postgres spits out:
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index
'journal_lines_pkey' for table 'journal_lines'
NOTICE:  CREATE TABLE will create implicit trigger(s) for FOREIGN KEY
check(s)
CREATE TABLE