This verse, from 1 Samuel 17:35, is part of David's recounting of his past experiences as a shepherd to King Saul. It describes his bravery and ability to protect his flock from wild animals. Let's break down the meaning:

"I went out after him, and struck him, and rescued it out of his mouth." This refers to David pursuing a lion or bear that had attacked one of his sheep. He confronted the animal, fought it, and managed to save the sheep from being eaten.
"When he arose against me, I caught him by his beard, and struck him, and killed him." This describes the animal's resistance. When the lion or bear retaliated and attacked David, he didn't back down. He grabbed it by its beard (an indication of close-quarters combat), struck it again, and ultimately killed it.

In essence, the verse illustrates David's courage, strength, and resourcefulness in protecting his sheep from predators. He presents this as evidence of his ability to face danger, which he then uses to convince Saul that he is capable of fighting Goliath.

Here are some important interpretations and implications of the verse:

Divine empowerment: Some religious interpretations view this passage as evidence of God's empowerment of David, preparing him for future challenges.
Leadership qualities: David's actions as a shepherd are seen as a metaphor for his future role as king, where he would protect and lead the people of Israel.
Contrast with Saul: David's bravery contrasts with Saul's hesitation to confront Goliath, highlighting David's faith and courage.
Exaggeration for effect? While some view this literally, others believe that the story might be slightly embellished to emphasize David's bravery and abilities. This was common in storytelling traditions of that time.

The story of David and Goliath is a powerful one about courage and faith.