Jesus went across enemy lines and shed his blood to cleanse us from all sin. In 2 Samuel 23, David's mighty warriors risked their lives to cross enemy lines and bring back water that David longed for from his hometown of Bethlehem. David refused to drink the water because the water represented the men's blood. There was a culture of love with David and his men. The culture of love starts with Jesus and he gave his life for us, so we should do things for the Lord out of an overflow of the example he set in love.
Colossians 3:23 tells us to "Work with all your heart at whatever you do, as though you were working for the Lord rather than for people." No matter what job or hobby you have, you can live for the Lord in all things. Jesus Christ is our motivation, and He endured the brutal beatings and crucifixion. As followers of Jesus, we look to God's Word so that we can have a biblical worldview for the cultural goliaths we face.
In the Bible, God uses the animal kingdom to teach us about wisdom. As powerful as lions are, God has given us human beings made in His image. Despite not looking the part, David was confident when he went against Goliath because he knew God was with him. When opposition comes our way, we can look to Jesus Christ, the author and perfector of our faith, and He makes us more Christlike.
Joab was a mighty military warrior under David, but he was flawed because he sacrificed his morals and did whatever it took, by any means necessary, to accomplish his purpose. As believers in Christ, we can't operate that way. We have to live differently and not follow the ways of the world. We are called to be Christ-like and we can't let our circumstances determine how we live this life.
Kindness may be viewed as a weak thing, but it is a fruit of the Spirit. In 2 Samuel 2, David showed kindness to his men and he looked out for their households because he cared deeply for them. Jesus showed us the ultimate kindness by sacrificing his sinless life for our sin-filled life so that we may be restored with God and have eternal life.