What does Mark 9:43 mean?

Jesus' words about a vague sin committed by a concrete body part parallels how scholars at that time spoke of concrete sins committed by an abstract body part, such as the heart. In Jesus' manner of speaking, the emphasis is placed on the choice, the action, and the responsibility of the perpetrator. The "hand" is a metaphor for the way in which the heart may lead the person to do something sinful.

The transition from Jesus' warning about causing others to sin in verse 42 is not as abrupt as it appears. Just as our heart may cause our hand to commit a sinful act, so it may cause a child or a younger Christian to commit a sinful act. Both require that we take serious steps to prevent our hearts from sinning.

The term translated as "hell" in English is literally tēn geennan. This is a reference to the Valley of Hinnom, the dump outside of Jerusalem where animal carcasses and other waste was burned. During the times of the worst idolatry in Israel, parents sacrificed their children to Molech by placing them in glowing-hot metal statues (Jeremiah 7:31; 19:5; 32:35). Good king Josiah tore down the altars and dedicated the valley to the burning of offal (2 Kings 23:10).

To "enter life" doesn't refer to being born. As "hell" means eternal punishment, "life" means eternal paradise for those who are saved by Christ. Jesus isn't giving a detailed description of eternity, here. Like in Matthew 5, He's illustrating how impossible it is to keep from sinning. Our resurrected bodies will not reflect the hardships we experienced in this life. Paul describes our new bodies as imperishable, glorified, and empowered (1 Corinthians 15:42–49).