"A thing that costs me nothing may nevertheless cost me much,. It may bring me under an obligation to the giver and so cost me more than it is worth. I may have so much trouble in appropriating it and keeping it that I may pay much more for it than the price which should be asked for it. "Nothing for nothing"
1Ch 21:24 And king David said to Ornan, Nay; but I will indeed buy it for the full price: for I will not take that which is yours for the LORD, nor offer burnt offerings without cost.
David was a man after God's own heart and yet he would not carelssly drop an offering in the plate so to speak. His love for God was real and his sacrice was going to be just that- an offering of love. We indeed need to have this same heart in every area of our life- our Lord is worthy of our best-selah.