What is the biblical basis for restitution? What is the New Testament Biblical basis for making restitution? I've read the story of Zacchaeus, and it's not completely set in stone as to what the structure is. The biggest question I have is if you've tried making restitution and the involved party won't accept your offer, should you do it anyway or is that "dishonoring" in any way?
The basis for making restitution is an Old Testament idea that is explicitly reiterated in the New Testament by Jesus.  When asked to summarize the law (the same law that he said he came to fulfill, not to abolish), Jesus uses an interesting formulation.  He said, 


  He answered, “‘Love the Lord your God with all your heart and with all your soul and with all your strength and with all your mind’[a]; and, ‘Love your neighbor as yourself.’[b]”


(This is in both Matthew and Luke)

In using this formulation, he was clearly drawing from Leviticus, a book we know he was thoroughly intimate with. (Not only here, but when he was tempted, etc...)  In using this formulation, he is explicitly pointing out that sin is sin against God and your neighbor, and as sin, it must be paid for. There are offerings, mentioned in Leviticus which come into play.

The OT basis for restitution

The biblical basis for restitution stems primarily from levitical law, and specifically, Leviticus 5 - 7. Leviticus 6, in particular looks to both the reasoning and the implementation of returning that which was taken, plus extra, to both the one offended and to the Lord against whom also the offender has sinned:


  6 [a]The Lord spoke to Moses: 2 “When someone sins and offends the Lord by deceiving his neighbor in regard to a deposit, a security,[b] or a robbery; or defrauds his neighbor; 3 or finds something lost and lies about it; or swears falsely about any of the sinful things a person may do— 4 once he has sinned and acknowledged his guilt —he must return what he stole or defrauded, or the deposit entrusted to him, or the lost item he found, 5 or anything else about which he swore falsely. He must make full restitution for it and add a fifth of its value to it. He is to pay it to its owner on the day he acknowledges his guilt. 
  
  6 Then he must bring his restitution offering to the Lord: an unblemished ram from the flock according to your assessment of its value as a restitution offering to the priest. 7 In this way the priest will make atonement on his behalf before the Lord, and he will be forgiven for anything he may have done to incur guilt.”


Restitution is a fairly simply property idea in law - a thief (however he took it) - should not be allowed to keep what he took, otherwise it makes a mockery of property rights.  Furthermore, the purpose of the law to is keep people from sinning against their neighbors as well as the Lord, so on the one hand, you don't want an incentive to sin, and on the other, you want clear consequences.

The Levitical approach, you will note, deals with both halves of the crime.

First, the victim gets his property back, plus profit (20% to be precise).  Not only does the thief not profit, he loses.  I find it interesting that the 20% "penalty" is equal to "two tithes," namely one for the Lord, plus one for the neighbor. 

Restitution for God is required

In addition to the victim's payment, however, restitution demands a sacrifice.  The linkage between the restitution offering and the sin offering is explicitly the same. As it says in Leviticus 7:


  The restitution offering is like the sin offering; the law is the same for both. It belongs to the priest who makes atonement with it. 


The idea in making the parallel explicit is that it highlights that sin is sin against both your neighbor and the Lord.  After David got Uriah killed so as to cover up his affair with Bathsheba, David makes an interesting statement:


  Against you, you only, have I sinned 
      and done what is evil in your sight; 
  so you are right in your verdict
      and justified when you judge. 


Now, I'll admit, I tend to think that David also sinned against Uriah, but the point is that David realizes the Lord is equally a party that need be satisfied for this sin.

Human forgiveness is optional. God's forgiveness is what counts

So, why do I keep hammering home the idea that one must "Love the Lord ... and Love your neighbor?"  Because, quite simply, forgiveness comes from the Lord.  If he has been satisfied with your attempt at restitution, you are forgiven. When you sinned, you sinned against two. If the greater one forgives, the lesser one's forgiveness isn't really that relevant. Sure, its nice if you can make up - but the sin was against the Lord, not your neighbor. 

I doubt, for example, that Zaccheus was able to return an exact accounting for the extra taxes he swindled in a precise 120% return to each individual that he had wronged. Logistically, accountingwise, pridewise (on the part of the victims) - it would have been daunting. But as Zaccheus proclaimed that he would give restitution, surely the Lord the was pleased.  That's the point. 

Restitution is an outward manifestation of an inward desire for repentance. It is a sign before God and man that the heart has changed. God forgives, man benefits. Both are offended, and the bigger one is clearly reconciled.