Do not stray after the thoughts of the heart and sight of the eyes (constant mitzvah)
“Do not follow after your heart and after your eyes’ Bemidbar 15:39
the heart and eyes are the agents of sin as the eye sees ,
the heart desires and the body commits the sin. -Rashi
We should not entertain in our heart any thought that can cause any of the main principles of our faith to be uprroted as the evil inclination will incite us to heresy, Heaven forbid.
“After the sight of your eyes” means immorality.
As the Sages taught Talmud Brachos 12b
After your heart means heresy and after your eyes means harlotry
This prohibition includes not to plan and pursue delights and cravings of this world.
It is extreamly necessary to be aware of reprehensible thoughts as this is the foundation from which everything eminates.
A person must sanctify and purify his thoughts with all his might.
If some type of forbidden pleasures come up he should have the intention that through this he should have the strength to stand in the palace of the Divine King , the Sovereign of the world and not let his body become weak in the service of the Creator
If a person transgressed and brought to mind -reprehensible thoughts regarding our faith or an immoral fantasy or to pursue material desires - this great sin will drive him out of the world to come.
It defiles all 248 limbs and 365 sinews that comprise the physical and spiritual.
A person must be extreamly vigilant with this.
This applies in all places and at all times for men and women.