Context: These words are the response of David to one of the most desperate prayers he ever uttered. Beginning/chapter: David foolishly (despite much pleading by Joab/others) decided to number his armies. When some kind of total was delivered to him, he was robbed of any satisfaction because his conscience smote him (v10) and soon he was to learn that God, although pardoning his sin, was still going to follow it through. Although David was given a choice of three punishments (v11-13) he very wisely decided to abandon himself into the merciful hand of the Lord (v14) and let God work out His own purposes.

God did so and in a short period many people, (70,000) country wide, perished (v15) By v16, the Destroying Angel is ready to wipe out the whole city of Jerusalem and it is here that David cries out in heart breaking prayer (v17) evoking this response from God (v18)

As David ran to do so, Araunah, upon enquiry, offered him free use of the threshing floor and oxen (v19-22) Here our text kicks in:
David refused the free gift, uttering the words/text and in the offering up of the sacrifice, the wrath/halted and the people went free: A wonderful picture/Calvary: Ephesians 1:14

We want to concentrate most on this thought of refusing to offer/God that which has not cost us anything. 4 thoughts:
By taking this position…

1) WE IMMEDIATELY MAGNIFY THE GLORY OF GOD:

A/ By presenting something in any circumstances which has not cost us anything, we can hardly claim any great credit for it
Indeed…it seems we are just passing on something we ourselves neither want nor have any room for.
We do it all with charity shops - pass on old clothes or bric a brac which has still some value to someone…but not to us
And in doing so, no thought: we have performed any great deed 
While we admire charity shops etc., yet we do not so elevate
them to an incredibly high position: Certainly not Deity
We do not speak reverently about them, meet weekly to sing hymns in their honour and offer prayer to them etc.,

B/ But we do so glorify God. Our admiration for Him knows no bounds. We profess ourselves to be His people. In an atheistic world, we are ready to defend Him, discounting all scorn etc.,
We fashion our lives by what He has said - In the passage (v11) Gad (The prophet) and David's own Seer (making it very personal)
carries great weight. No mention now of King's word prevailing (v4) There's only one King here who is speaking:
The LORD is King for ever and ever: (Psalm 10:16)
David (by his own desire) has surrendered and fallen into His hand, pleading and hoping/yearning for His sovereign mercy

C/ In such circumstances, is it glorifying/God to give Him something which has cost us something?
Two ways of measuring cost
[i] World's way. Sheer value without any regard to ability/pay
Thus a rich man who writes the highest cheque gives most
[ii] God's way. The one who gives the most is the widow who casts into both mites  - even all her living and Jesus says:
Of a truth I say unto you, that this poor widow hath cast in more than they all: For all these have of their abundance cast in unto the offerings of God: but she of her penury hath cast in all the living that she had. (Luke 21:4-5)

D/ God doesn't need anything from us. Strictly speaking, God does not derive all His glory from us, but only manifests His own glory, in, by, unto and upon us 
Therefore it is more God honouring, if we decline to give Him the dregs of what we have no longer any use for and give Him that which is sacrificial and which costs us dear.
Don't take short cuts with God. Don't relegate Him down the list/ Don't just fit Him in somewhere when/if you can
Don't give Him that which has cost you nothing.

2) WE IMITATE HIS GIVING TO US:

A/ Not to suppose that it took any great effort/God's part to create the world - a word/sufficed - nor to keep this world up and running. I am the Almighty God! (Genesis 15:1)

B/ But we may assume that He felt it keenly when he parted with His only Begotten Son and sent Him into the world

[i] For a past eternity, His Son lay in the Father's bosom (John 1:18) and could say: Then I was by him, as one brought up with him: and I was daily his delight, rejoicing always before him; (Proverbs 8:30) He is called "His dear Son" or "Son of His love" (Colossians 1:13) Declared of Him publicly: "My Beloved Son in whom I am well pleased" (Matthew 3:16) His elect servant in whom his soul delighted (Isaiah 42:1) 

[ii] We might think as to why the Father sent the Son and what it entailed. To be the Saviour/world entailed the bearing away of the Sin/World. Involved the awful suffering/Calvary when the Father would turn away His holy face and forsake Him (Matthew 27:46) This only after He had been despised/rejected of men and subject to all the infirmities/flesh (sin apart) for 30+ years

C/ Yet the Father never pulled back once. He did not make do with a lesser Being - like Michael or Gabriel - nor did He sacrifice the whole host/angels in their millions for this great end
No, He sent His only begotten Son into the world, that we might live through Him. In giving Christ, He gave everything He had

D/ What can we give, when it can be said that we gave our all?
Immediate answer: Our hearts in accordance with Proverbs 23:26
If we give all except our hearts…He isn't really interested
I don't know if this is strictly kosher (doctrinally) but if not, excuse it on devotional grounds: Christ is the heart/God
We see the kindly face of God in Jesus Christ - Not that God the Father or God/Holy Spirit are not kindly…but this kindness is channelled to us through Christ
When you have given God your heart, then everything you have will be His also, at His disposal.
But to give Him something which is the moral equivalent to the small change in the bottom/pocket is not to imitate Him at all and we are falling short if we profess to be godly people

3) WE LAY UP TREASURE IN HEAVEN:

A/ God is a gracious God. Strictly speaking, we don't give to Him at all, but we only give back what is rightfully His anyway. To
hold back is thus said to "rob God" (Malachi 3:8)
Positively: David said: But who am I, and what is my people, that we should be able to offer so willingly after this sort? for all things come of thee, and of thine own have we given thee. (1 Chrons 29:14)
At best we are always unprofitable servants with nothing to give

B/ But God graciously rewards us for giving Him back what He already owes. He rewards good stewardship and acts against poor stewardship. This is purely, solely on the basis of grace
His name is love and grace is the brightest jewel/His crown

C/ If we give Him that which costs us nothing, then do not expect a greater reward/Heaven. If we sow sparingly, then we will also reap sparingly, but if we sow abundantly etc.,
(2 Corinthians 9:6) He gives it back to us in Heaven
[i] Where all is everlasting. Earthly riches fly away
[ii] Where they are safe - No thief breaks through to steal
[iii] Where it cannot disappoint cp. earthly riches
[iv] Where much more is given than we ever give Him

4) WE MAKE A STATEMENT WHICH WILL AT ONCE SPEAK BOTH TO SAVED AND UNSAVED ALIKE:

A/ David was under great pressure as he negotiated/Araunah
70,000 people had already perished and the Angel/Lord had his sword drawn over Jerusalem ready to go again
But it wasn't a matter: whatever came to hand/anything will do
David was going to do it right and have the price paid

B/ When we give the Lord that which has cost us (as opposed to the little things which we hardly wanted anyway) we send out a message to the unsaved: This matter is serious.
Christianity isn't a hobby type interest. Not a mere pastime, although you can reduce it to such and make it a travesty, it is a life. It is not something you do...but something you are.
The world wants to play it all down. Wants to rob God of all that he is so that they can sin without any real worries. It is no service to the unsaved to let them think like that.

C/ What a message to other Christians when you can effectively say: "For me to live is Christ…" (Philippians 1:21) Many of those real dedicated Christians have encouraged me. Give Him all.