The subject may be a bit dark for the website but in plain view of reasoning, the line of reason is that:
- People who masturbate often look at women with lust.
- For masturbation to occur (in general) people must use the hand.
- Today, there is pornography. At Jesus' times the only way people could masturbate while thinking (in the heart/mind) about women was to first look at them.
- What often causes people to masturbate is looking with a lustful intention.
The passage reads:
“You have heard that it was said, ‘YOU SHALL NOT COMMIT ADULTERY’;
28 but I say to you that everyone who looks at a woman to lust for her has already committed adultery with her in his heart.
29 Now if your right eye is causing you to sin, tear it out and throw it away from you; for it is better for you to lose one of the parts of your body, than for your whole body to be thrown into hell.
30 And if your right hand is causing you to sin, cut it off and throw it away from you; for it is better for you to lose one of the parts of your body, than for your whole body to go into hell.
I reason that Jesus considers the action higher than the intention, for the parable of two sons when one said he would work but didn't, the other said he wouldn't but did, the latter did his father's will.
Along with other passages mentioning that the body/flesh constantly desires pleasure and John teaching to deny the lust of the eye, implying that the eyes does lust.
1 John 2:16 For all that is in the world, the lust of the flesh and the lust of the eyes and the boastful pride of life, is not from the Father, but is from the world.
The question is, is it possible that the passage is talking about the act of masturbation?