As the beginning of the parsha starts b'lashon yachid, the chida explains that each individual must appoint shoftim and shotrim for all his body's 'gateways' to the world. Some say it is the senses others say the openings - eyes ears mouth and nose. I heard from Rabbi Zucker אלול is roshei teivos אחת למעלה ושבע למטה - the mind that is above the body must overcome the seven below.
Later - 20.1 - when you go to war and see the horses, chariots, and עם רב ממך dont fear them... The balei drush say this hints to the war of the yetzer hara. Two psukim later the kohein warns 'don't be soft hearted, don't fear, don't tremble and dont feel broken' . These total seven warnings!
Id like to suggest the first three are actual enemies - the 3 cardinal midos and sins קנאה תאוה וכבוד the hose is gavah. Rechev is tavah (pituchei chisum says ut is the shaidah - lilis) and am rav mimcha is kinah - the many that the others have.
The latter four are not real. They are the psychological warfare. Dont be scared or broken hearted etc. The satan may excite us or bring us to despair.
Another hint of אלול is לולא האמנתי 'if only or hal'vai'. We have to use achas lmalah our 'hech'reh musagim' against the sheva l'mattah.
If the satan can appetize us with our imagination we must appetize our minds as well by reading some mussar that offers loftiness. One l'malah can overpower the lmatah even if its outnumbered 7 to 1. Perhaps just a little daily exposure to lofty mussar (2 minutes a day after mariv?) can overthrow all the lowly exposure weve had a whole day.