Halakhah su Giudici 14:78

He prohibited us that we not wander after our hearts to the point that we believe doctrines that are the opposite of the doctrines that the Torah obligates us. Rather we must restrain our thoughts and place a boundary against them to stand thereby - and that is the Torah's commandments and its prohibitions. And that is His saying, "and you shall not wander after your hearts and after your eyes" (Numbers 15:39). And the language of the Sifrei (Sifrei Bamidbar 115:1) is, "'After your hearts' - that is heresy, as the matter that is stated (Ecclesiastes 7:26), 'And I find more bitter than death the woman (understand to mean heresy), etc.' 'And after your eyes' - that is promiscuity, as the matter that is stated (Judges 14:3) 'Take her for me, for she is just in my eyes.'" [This is] meaning to say, being drawn after physical desires and mental involvement with them. (See Parashat Shelach; Mishneh Torah, Foreign Worship and Customs of the Nations 2.)

To not wander after the thoughts of the heart and the vision of the eyes: That we not wander after the thoughts of the heart and the vision of the eyes, as it is stated (Numbers 15:39), "Do not wander after your hearts and your eyes." The content of this negative commandment is that we were prevented from dedicating our thoughts to think about opinions that are antithetical to the ones on which the Torah is built, as that may lead one to apostasy. Rather, if the spirit to pursue these bad opinions should arise, one should minimize his thinking about them, and redouble his efforts to contemplate the true and good ways of the Torah. Similarly, one should not pursue the things he sees; and included in this is that we not pursue after the desires of this world, for in the end they are evil and 'there is much shame and wrath.' This is [the meaning of] what they, may their memory be blessed, said (Berakhot 12b), "'Do not stray after your hearts' refers to apostasy. 'After your eyes' refers to licentiousness, as it is stated (Judges 14:3), 'And Samson said to his father, "Take her for me, as she is right in my eyes."'"