OT BGAII 3.41 (or version 3) by Srila Prabhupada:

3.41 Therefore, O Arjuna, the best among the descendants of Bharata, from the very beginning curb the great symbol of sin (lust) by regulating the senses because it is the destroyer of knowledge and specifically knowledge of the self.

Purport. The Lord advised Arjuna to regulate the senses from the very beginning so that one can curb the greatest sinful enmy, lust, which destroys the urge for self realization and specific knowledge of the self. Jnanam means knowledge of the self and the non-self or in other words to know that the spirit soul is not the body and vijnanam means to know the specific knowledge of the spirit soul, namely his constitutional position and his relatiosnhip with the Supreme Soul Personality of Godhead. In the Srimad Bhagavatam (2.9.31) it is explained as follows: 

sri bhagavan uvaca

jnanam parama-guhyam me

yad vijnana-samanvitam

sarahasyam tad-angam ca

grihana gaditam maya

“The knowledge of the self and the Supreme Self is very confidential and mysterious, and with different paraphernalias and such knowledge and specific realization can be understood if they are explained by the Lord Himself.” 

Bhagavad Gita represents that general and specific knowledge of the self. The living entities are parts and parcels of the Lord, and therefore they are simply meant for serving the Lord. This consciousness is called Krishna consciousness. So from the very beginning of life, one has to learn this Krishna consciousness, and thus one may become fully Krishna conscious and act accordingly. As explained above, lust is only the perverted reflection of love of Godhead which is natural for every living entity. If, therefore, he is educated in the matter of Krishna consciousness from the very beginning, then that natural love of Godhead cannot deteriorate into lust. When love of Godhead becomes deteriorated into lust, it is very difficult to get it back to its normal condition. But still Krishna consciousness is so powerful that even a late beginning can also turn one into a lover of Godhead through the regulative principles of devotional service. So, from any stage of life, or from the time of understanding its urgency, one can begin regulating the senses in Krishna consciousness devotional service of the Lord, and turn back the lust into love of Godhead—the highest perfectional stage of human life.

Jayadvaita sees:

3.41 Therefore, O Arjuna, best of the Bharatas, in the very beginning curb this great symbol of sin [lust] by regulating the senses, and slay this destroyer of knowledge and self-realization.

PURPORT
The Lord advised Arjuna to regulate the senses from the very beginning so that he could curb the greatest sinful enemy, lust, which destroys the urge for self-realization and specific knowledge of the self. Jnana refers to knowledge of self as distinguished from non-self, or in other words, knowledge that the spirit soul is not the body. Vijnana refers to specific knowledge of the spirit soul’s constitutional position and his relationship to the Supreme Soul. It is explained thus in the Srimad-Bhagavatam (2.9.31):
jnanam parama-guhyam me
yad vijnana-samanvitam
sa-rahasyam tad-angam ca
grhana gaditam maya
“The knowledge of the self and Supreme Self is very confidential and mysterious, but such knowledge and specific realization can be understood if explained with their various aspects by the Lord Himself.” Bhagavad-gita gives us that general and specific knowledge of the self. The living entities are parts and parcels of the Lord, and therefore they are simply meant to serve the Lord. This consciousness is called Krsna consciousness. So, from the very beginning of life one has to learn this Krsna consciousness, and thereby one may become fully Krsna conscious and act accordingly.
Lust is only the perverted reflection of the love of God which is natural for every living entity. But if one is educated in Krsna consciousness from the very beginning, that natural love of God cannot deteriorate into lust. When love of God deteriorates into lust, it is very difficult to return to the normal condition. Nonetheless, Krsna consciousness is so powerful that even a late beginner can become a lover of God by following the regulative principles of devotional service. So, from any stage of life, or from the time of understanding its urgency, one can begin regulating the senses in Krsna consciousness, devotional service of the Lord, and turn the lust into love of Godhead — the highest perfectional stage of human life.

And Hayagriva sees:

3.41 Therefore, O Arjuna, best of the Bharatas, in the very beginning curb this great symbol of sin [lust] by regulating the senses, and slay this destroyer of knowledge and self-realization.

PURPORT
The Lord advised Arjuna to regulate the senses from the very beginning so that he could curb the greatest sinful enemy, lust, which destroys the urge for self-realization, and specifically, knowledge of the self. Jnanam refers to knowledge of self as distinguished from non-self, or, in other words, knowledge that the spirit soul is not the body. Vijnanam refers to specific knowledge of the spirit soul and knowledge of one’s constitutional position and his relationship to the Supreme Soul. It is explained thus in the Srimad-Bhagavatam: jnanam parama-guhyam me yad-vijnana-samanvitam / sarahasyam tad-angam ca grhana gaditam maya: “The knowledge of the self and the Supreme Self is very confidential and mysterious, being veiled by maya, but such knowledge and specific realization can be understood if it is explained by the Lord Himself.” Bhagavad-gita gives us that knowledge, specifically knowledge of the self. The living entities are parts and parcels of the Lord, and therefore they are simply meant to serve the Lord. This consciousness is called Krsna consciousness. So, from the very beginning of life one has to learn this Krsna consciousness, and thereby one may become fully Krsna conscious and act accordingly.
Lust is only the perverted reflection of the love of God which is natural for every living entity. But if one is educated in Krsna consciousness from the very beginning, that natural love of God cannot deteriorate into lust. When love of God deteriorates into lust, it is very difficult to return to the normal condition. Nonetheless, Krsna consciousness is so powerful that even a late beginner can become a lover of God by following the regulative principles of devotional service. So, from any stage of life, or from the time of understanding its urgency, one can begin regulating the senses in Krsna consciousness, devotional service of the Lord, and turn the lust into love of Godhead — the highest perfectional stage of human life.

Notwithstanding the variation between the three different renditions, the idea is that lust is directly connected to love of Godhead. Kama as in Kama Sutra stands for lust. People often cheaply joke about Kama Sutra when I present Bhagavad Gita As It Is. Prema as in prema pumartho mahan. SB 3.23.8:”Lord Caitanya recommended that the greatest achievement of human life is to achieve the grace of the Lord, love of God. He said, prema pumartho mahan: to achieve love of Godhead is the highest perfection of life.”

So lust is an enemy because it destroys the urge for self realisation as well as specific knowledge of the self. Specific knowledge of the self refers to the constitutional position of the self in relation to “the Supreme Soul Personality of Godhead”- Srila Prabhupada’s expression.