The laws of Leviticus provide an insight into the heart and values of the law giver. So when attempting to give back to God you need to have an understanding of who you are approaching. If you are bringing a tribute to a king and your gift is filthy, soiled and tattered rags, your gift is offensive and so you should expect to be in trouble if not hanged for your offense. In the workplace if you were to give your boss, teacher, or friend a case of deodorant and mouthwash, they are likely to be offended that you believe them to stink in some manner. Or if you know your friend likes video games but hates crossword puzzles, it is just wrong to offer them crossword puzzles as a gift. So the laws of Leviticus like other laws throughout scripture are not just what to do and not to do, but are insights into the things that please and displease God. So if God requests sacrifice there is no wonder that it should be without blemish or spot, because He is holy and so without blemish and spot. Most people do not go out of their way to offend their friend, loved ones and those we report to, but we find it so easy to offer God less than our best. Offering just anything will not do (Malachi 1:6-14)
As mentioned we also get a picture of the values of God through the laws He established.
“And when you reap the harvest of your land, you shall not reap your field right up to its edge, nor shall you gather the gleanings after your harvest. You shall leave them for the poor and for the sojourner: I am the Lord your God.” – Leviticus 23:22, 19:9
What is this law trying to convey? It is establishing a premise of care for those who are poor or passing through your area. It is also establishing that it is wrong to be greedy as if you need to harvest two maybe three times to ensure you collected all that you can. So it establishes also that although you leave some of a crop behind for others, your trust in commerce and self preservation comes from God who gave the crop in the first place. All these things give us the principles of where God says our heart should be in relation to Him and to our fellow man. These are not merely Old Testament and so passé ideals. We take these forward and still understand that God values our looking after the poor, that we too should make some provision for those who are less fortunate than ourselves. We are not to put our trust in wealth, but still tithe happily knowing that it is God who still sustains us and knows our needs even before we ask. God’s values have not changed. Sure we do not go back to the Old Testament law and start building fences on our roofs, as they were literally instructed to do. But the equity of the command in which it serves to protect people is the same cares we need to have in our day in providing fences to protect people from the harm of say a tall building, work area, or pool.