1 The LORD is my shepherd, I shall not be in want. 2 He makes me lie down in green pastures, he leads me beside quiet waters, 3 he restores my soul. He guides me in paths of righteousness for his name's sake. 4 Even though I walk through the valley of the shadow of death, I will fear no evil, for you are with me; your rod and your staff, they comfort me. 5 You prepare a table before me in the presence of my enemies. You anoint my head with oil; my cup overflows. 6 Surely goodness and love will follow me all the days of my life, and I will dwell in the house of the LORD forever. - Psalm 23

"The LORD is my shepherd"
To me this means Believers in Christ Jesus are His sheep.  In addition, The LORD is called the Believer's "great shepherd" in Hebrews 13:20 probably in reference to this Psalm.

"I shall not be in want"
This condition is because if you have a relationship with the "Great Shepherd" you have everything.  However, within His fold, flock, and/or Kingdom there are many additional Benefits - 

1.  "He makes me lie down in green pastures"
The Great Shepherd treats His sheep to "green pastures", representing the opportunity for the sheep to graze and rest.  So, applying that to the Believer - "He makes me lie down in [His provision, His daily bread and comfort/rest]"  

2.  "He leads me beside quiet waters" 
As a sheep, "quiet waters" would nourish the inside with nice, cool, refreshing water and calm the outside by being a pleasant sound to hear.  It would also not drown out any potential predatory threats like raging waters or rapids would.  For the Believer another verse helps out here - "Peace I leave with you, my peace I give unto you: not as the world giveth , give I unto you. Let not your heart be troubled , neither let it be afraid." (John 14:27)  Concerning "quiet waters" that anyone would want to dwell beside or drink from - "Jesus answered, "Everyone who drinks this water [water from a human well] will be thirsty again, but whoever drinks the water I give him will never thirst. Indeed, the water I give him will become in him a spring of water welling up to eternal life." (John 4:13-14)  The Words of Jesus are indeed The Bread of Life and The Living Water of the soul and the "quiet waters" is a great place for meditation and nourishment from the River of Life Himself - Jesus.

3.  "He restores my soul" 
As a shepherd might console or comfort a sheep that is agitated about something so does the Believer's Great Shepherd with His flock.  Jesus is also known as the Prince of Peace (Isaiah 9:6) and through the power of the Holy Spirit He ministers to the Believer, restoring their souls when needed.  However, the ultimate restoration comes for the "whosoever will believe" (John 3:16).  Jesus has taken the condition of everyone's soul - Broken - and restored it for eternity.

4.  "He guides me in paths of righteousness for his name's sake." 
A regular human shepherd would guide a sheep along the right path.  The Great Shepherd of the Believer in Christ not only leads us along the right path, but the path we traverse is of "righteousness" or right doing and it is "for his name's sake" or for the Glory of God that we do.  Notice too that sheep may bear a mark of their shepherd.  The Believer has the responsibility of carrying and representing the name of Jesus Christ - Christian.  The Lord guides the true Believer along the journey of life in doing the right thing so that other people might say, "Hey, He/She must be a Christian because that lines up with what the Bible and I have believed a Christian should do."  We bear His name, use it wisely and not in vain!

5.  "Even though I walk through the valley of the shadow of death, I will fear no evil, for you are with me;"  
Wow!  There is the "shadow of death" and then there is "the valley of the shadow of death"!  And even though Believers may reach a point in their lives where they are facing their mortality and possibly see evil itself - there is no need for any kind of fear, including the fear of evil because The Great Shepherd is with us (the Believers).  In fact, The Great Shepherd has hand-held devices that help this cause.

6.  "your rod and your staff, they comfort me."
A shepherd would use a "rod", a straight club, to defend his sheep.  His staff, the hooked rod or inverted "J" that we commonly see shepherds pictured with are used to guide sheep or pull them back from danger. So it is with the Great Shepherd of the Believers in Christ.  He does the same mentally, physically, and spiritually for His flock.

7.  "You prepare a table before me in the presence of my enemies." 
As a sheep I am elated I am not on the menu!  I am so happy the table has not been prepared for me to be the main course for someone!  No!  On the contrary!  The table is prepared before my enemies so they can see that I have "tasted of the Lord and He is good!" (Psalm 34:8)  They will see that I and many other Believers have partook of the Lord's Table, believing in The Sacrificial Lamb - Jesus, that we have taken into our lives as our Savior, The Lamb of God (John 1:29).

8.  "You anoint my head with oil"
This is a special sheep for sure, if you keep that theme here.  From a sheep to a priest!  In the Old Testament whenever a Priest or King was ordained, someone anointed him.  Revelation 20:6 views the Believer as Priests, anointed to rule and reign with Christ during the Millennial Reign of Christ on earth - "Blessed and holy are those who have part in the first resurrection. The second death has no power over them, but they will be priests of God and of Christ and will reign with him for a thousand years." 

9.  "my cup overflows"
The Great Shepherd has done everything for the sheep or Believer in this Psalm.  There are times in our lives when we need to not only stop and smell the roses, but we need to pause and know that He is God (Psalm 46:10).  However, there are other instances where action on our part is required first.  "Bring ye all the tithes into the storehouse, that there may be meat in mine house, and prove me now herewith, saith the LORD of hosts, if I will not open you the windows of heaven, and pour you out a blessing, that there shall not be room enough to receive it." (Malachi 3:10)  "Give, and it will be given to you. A good measure, pressed down, shaken together and running over, will be poured into your lap.  (Luke 6:38) 
"Surely goodness and mercy shall follow me all the days of my life,"
With good attention and merciful behavior from any regular shepherd the sheep are sure to flourish.  How much more so the flock under the care of the "goodness and mercy" of The Great Shepherd!  And not just this....

"and I will dwell in the house of the Lord forever."
And His house is to die for!  ;)