I think this may be a good answer for youI Samuel 17:40 "And he took his staff in his hand, and chose him five smooth stones out of the brook, and put them in a shepherd's bag which he had, even in a scrip: and his sling was in his hand:"Stop and consider this armor that David it taking into battle. David took the wooden stick called his staff that he had tended his sheep with, and he selected five smooth stones from the brook that ran through the valley. Remember that the trenches of the troops are at the top of the hill, and the brook is down in the valley. David moved out of the trench and down into the valley to prepare for the warfare. David moved with the faith that God would see him through, and provide those stones for his battle with Goliath. David selected these five smooth stone and put them in his shepherd's bag that he was carrying.Even though David only used one stone to do the job, He selected five stones. This starts the understanding of "the key of David", for the number five represents "grace". It is through the grace of the Father, and through His Son, Jesus Christ, the offspring of David that we find salvation. He is the hidden manna that we read of in Revelation 2:17. Revelation 2:17 "He that hath an ear, let him hear what the Spirit saith unto the churches. To him that overcometh will I give to eat of the hidden manna, and will give him a white stone, and in the stone a new name written, which no man knoweth saving he that receiveth it:"Meaning those that partake of this Word and truth, in a Spiritual sense, God would give a "white stone" with a new name written thereon. And that Greek word used for "stone", is a similar word for the word "count", in Revelation 13:18. The two verses are tied together for to have the white stone is to be able to count the number of the beast. The "hidden manna" is the truths from the Word of God that only those with ears to hear with understanding will know their meaning. Revelation 13:18 "Here is wisdom. Let him that hath understanding count the number of the beast: for it is the number of a man; and his number is Six hundred threescore and six."This is God's way of teaching his elect as to how they were to "count the number of their enemy". Goliath as seen here in I Samuel was only a type of the enemy. Though the enemy may look like a giant to many in our day, they are not to you when you understand God's Word. So lets go to Strong's Greek dictionary for the correct translation from the Greek to English, as used here in the Scripture. #5585; "Psephizo, psay-fid'-zo; from 5506; to use pebbles in enumeration, i.e. to compute:-to count." So lets go to the root word to understand the full meaning of this word in $5586; "Psephos, psay'-fos: from the same as 5584: a pebble (as worn smooth by handling), i.e. (by impl. of use as a counter or ballot) a verdict (of acquittal) or ticke (of admission); a vote: stone, voice."This is simply saying, the elect are to keep up with the identity of the children of Cain down through the many generations of time to be able to identify them and their activity. To be able to identify the evilness that they bring with them on the peoples that they have mixed with. When you know where these Kenites are, you will understand that where they, they will be promoting their father, the false messiah, which is the devil himself. The Kenites are those smooth stones worn smooth over a very long period of time, and even in our generation, when you see their way of doing things and the things they are saying, it is to promote the ways of Satan. So to have the "key of David", is to be able to identify the true from the false, to be able to identify the things of God, from the twisted truth, that have become nothing but lies and do not come from the Word of God. When you have the "key of David", you will be able to know when the truth from God's Word is being made into a lie by the word smiths that like to twist the truth to make it a lie. Do you have the "white stone", for that white stone is your weapon, in a spiritual sense. The church in the latter times that had the key of David are those that taught as the church of Philadelphia. Revealtion 3:7 And to the angel of the church in Philadelphia write; `These things saith He That is Holy, He That is true, He That hath the key of David, He That openeth, and no man shutteth, and shutteth, and no man openeth."It gives you an advantage in these final days of this earth age, and even David had this advantage. The advantage was not because of the stone that he selected, but because He knew our Heavenly Father. David knew the things of the Father from those things of the world. David knew that what was about to happen was in accordance with God's plan, and that God would protect him. After all Samuel had just anointed him king, and David had faith.
http://www.theseason.org/1Samuel/1Samuel17.htm