The gift is acceptable according to what one has,

2 Corinthians 8:1-15
But since you excel in everything—in faith, in speech, in knowledge, in complete earnestness and in the love we have kindled in you—see that you also excel in this grace of giving.
For if the willingness is there, the gift is acceptable according to what one has, not according to what one does not have.
At the present time your plenty will supply what they need, so that in turn their plenty will supply what you need. The goal is equality, as it is written: “The one who gathered much did not have too much, and the one who gathered little did not have too little.”
Now that confidence is restored, it is possible to raise the matter of the relief fund for the poor in Jerusalem. Titus had helped the Corinthians make a start, following Paul's instructions in his earlier. Now he is to return and supervise the accompanied  by delegates from the Macedonian churches as a safeguard against any charge that Paul was embezzling the fund.
Why?
We need not only the gift of spirit but also in grace of gift.
God hope we give in our desire, but not command. which may reach the goal of equality. 
For what I lack which may lead us keep it more, but Paul teach us give may get more grace from the Lord.
Jesus has loved me, when I really know the love of the Lord! Then I will like to give!
How?
Give for what I have to the needed person, because God loves us.