¹¹ In ancient times, watchmen worked closely with city gatekeepers. (2 Sam. 18:24-26) Together, they helped protect the city by making sure that the gates were closed whenever an enemy came near. (Neh. 7:1-3) Our Bible-trained conscienceb can act as our watchman and warn us when Satan tries to invade our heart​—in other words, when he tries to influence our thoughts, feelings, motives, or desires. Whenever our conscience sounds the alarm, we need to listen and shut the gate, so to speak.

12-13. What might we be tempted to do, but how should we react?

¹² Consider an example of how we can protect ourselves from being influenced by Satan’s thinking. Jehovah has taught us that “sexual immorality and every sort of uncleanness [should] not even be mentioned among [us].” (Eph. 5:3) But what will we do if peers at work or at school start talking about sexually immoral topics? We know that we should “reject ungodliness and worldly desires.” (Titus 2:12) The watchman, our conscience, might sound an alarm. (Rom. 2:15) But will we listen to it? We might be tempted, instead, to listen to our peers or to look at pictures they might be sharing. But this is the time to close the city gates, so to speak, by changing the conversation or by walking away.

14-15. (a) To what do we need to open our heart, and how can we do so? (b) How does Proverbs 4:20-22 help us to get the most out of our Bible reading? (See also the box “How to Meditate.”)

¹⁴ To safeguard our heart, we must not only close it to wrong influences but also open it to positive influences. Think again about the illustration of a walled city. A gatekeeper closed the gates of the city to stop an enemy invasion, but at other times he opened the gates to allow food and other supplies to be brought in. If the gates were never open, the inhabitants of the city would starve. Similarly, we need to open our heart regularly to the influence of God’s thinking.