God, because of the deadly consequence of sin has given us His Word to keep us from sin. Referring to the Bible, John Bunyan wrote "Either this book will keep you from sin or sin will keep you from this book". The word of God purifies and cleanses us from all sin when we simply obey the commandments of the Lord. God's word is life and rescues man from the power of sin and spiritual death.
You can tell whether someone is a Christian or not by their life and walk: a good tree cannot bring forth evil fruit, neither can a corrupt tree bring forth good fruit. Genuine Christians live and walk in the Spirit. They walk circumspectly, not allowing the flesh to have dominion over them.
David was truly a man after God's heart. He feared the Lord and endeavoured to obey His word. The incident in the text above is just one of the many opportunities that David had to kill Saul who was after his life, but he would not. He realised that Saul was the Lord's anointed and that nobody ever touches the Lord's anointed and goes scot-free.
To be like your heavenly Father, the Lord commands you to love your enemies, bless them that curse you, do good to them that hate you, and pray for them that despitefully use you and persecute you. Remember that man was originally created in the image of God. Unfortunately, the power to overcome evil with good and all the virtues of godliness were lost as a result of the fall of man.
While the disciples who witnessed the ascension of Jesus Christ, stood gazing into heaven, they were informed by two angels, that the same Jesus will come back again. Since then, many deceivers born of women have presented themselves to the world as Jesus. But we are expecting the same Jesus that ascended into heaven, to come back in like manner by descending from heaven to rapture his bride: "for the Lord himself shall descend from heaven ..." - 1 Thessalonians 4:16-17.