In Matthew, Mark, and Luke 1 out of every 6 verses deals with money. Of the 29 parables Christ told, 16 deal with a person and his money.
Giving to the lord was established all the way back in the book of Genesis When abel brought his sacrifice unto the Lord
Then under the law the children of Israel would bring a tithe or a tenth of all that they had to the lord.
Leviticus 6:15-19 And he shall take of it his handful, of the flour of the meat offering, and of the oil thereof, and all the frankincense which is upon the meat offering, and shall burn it upon the altar for a sweet savoir, even the memorial of it, unto the Lord.  And the remainder thereof shall Aaron and his sons eat: with unleavened bread shall it be eaten in the holy place; in the court of the tabernacle of the congregation they shall eat it
Leviticus 27:30 And all the tithe of the land, whether of the seed of the land, or of the fruit of the tree, is the Lord’s: it is holy unto the Lord.
Exodus 35:5 (KJV)
Take ye from among you an offering unto the Lord: whosoever is of a willing heart, let him bring it, an offering of the Lord; gold, and silver, and brass,
Exodus 36:6 (KJV)
And Moses gave commandment, and they caused it to be proclaimed throughout the camp, saying, Let neither man nor woman make any more work for the offering of the sanctuary. So the people were restrained from bringing.
Exodus 36:7 (KJV)
For the stuff they had was sufficient for all the work to make it, and too much.
I do not believe one can settle how much we ought to give. I am afraid the only safe rule is to give more than we can spare.
The American industrialist, Henry Ford, was once asked to donate money for the construction of a new medical facility. The billionaire pledged to donate $5,000. The next day in the newspaper, the headline read, "Henry Ford contributes $50,000 to the local hospital." The irate Ford was on the phone immediately to complain to the fund-raiser that he had been misunderstood. The fund-raiser replied that they would print a retraction in the paper the following day to read, "Henry Ford reduces his donation by $45,000." Realizing the poor publicity that would result, the industrialist agreed to the $50,000 contribution in return for the following: That above the entrance to the hospital was to be carved the biblical inscription: "I came among you and you took me in."
We give to support the ministry
The Old Testament system of supporting the ministry was brought into the new testament church. Paul 9:9-20 (ESV)
For it is written in the Law of Moses, "You shall not muzzle an ox when it treads out the grain." Is it for oxen that God is concerned?  Does he not speak entirely for our sake? It was written for our sake, because the plowman should plow in hope and the thresher thresh in hope of sharing in the crop.  If we have sown spiritual things among you, is it too much if we reap material things from you?  If others share this rightful claim on you, do not we even more?
Nevertheless, we have not made use of this right, but we endure anything rather than put an obstacle in the way of the gospel of Christ.  Do you not know that those who are employed in the temple service get their food from the temple, and those who serve at the altar share in the sacrificial offerings?  In the same way, the Lord