Zakath,
The Hebrew nation was a theocracy when it was first established. Thus their whole government was based upon laws given by God.
I agree that lending money at interest to each other was not allowed by their civil law. And that is what it is, a civil law. While it's foundation is built upon the same principles that underly the ten commandments it is separate from the that law.
Everything in the Hebrew economy had a point. God taught a lesson in each and every law He gave, and in each and every symbol in thier system of worship. In that system of worship the Ten Commandments were placed inside the Ark of the Covenant, underneath the mercy seat which symbolizes the mercy of God in forgiving sin. On the outside of the Ark of the Covenant, on each side of the Ark were place to pockets, if you will, and in those pockets were placed the copy of the civil law that was given to Moses by God. This was done at God's instruction.
Now, it's clear that by doing this that God is making a distinction between the two laws, for everything in the sanctuary was symbolic of something. Everything that was placed in the sanctuary had specfic meaning, and even the placement of each object within the two rooms had specific meaning. From this we see that God did indeed have separate purposes and goals for the ten commandments and the civil laws.
Paul said that the law of ordinances that was against us was set aside by Christ, and that now the wall between the Jew and Gentile was broken down. Now, how could that have included the ten commandments as they had always been shown to have been covered by God's mercy by the symbolism of the sanctuary? The Ten Commandments do not create a separation between Jew and Gentile. They address the heart condition of all mankind. They are the schoolteacher that brings us to a knowledge of our need of a Savior. Thus the law of ordinances set aside is the civil law.
Notice what Jesus said at the beginning of His ministry in relation to the temple.
Joh 2:16 And said unto them that sold doves, Take these things hence; make not my Father's house an house of merchandise.
Compare that with the statement he made concerning the temple at the end of His ministry.
Luk 13:35 Behold, your house is left unto you desolate: and verily I say unto you, Ye shall not see me, until the time come when ye shall say, Blessed is he that cometh in the name of the Lord.
Thus we see a change being made. God is saying, this time, the time of the Jews, is past, and then we see Paul speaking of the time of the Gentiles. What had once defined and shown the presence of God, the temple and all it stood for, was no longer blessed by His presence. It had become an empty shell. God's grace and mercy hadn't changed, but He left behind those who would not follow Him.
The Jewish/Hebrew nation had been created/organized for the purpose of showing the world who God is. When the Jews finally rejected Christ they were set aside as that organization, and the Christian church became the organization to be used of God to spread the Gospel and the knowledge of Himself. Thus, as the nation of Isreal was no longer the organization that one needed to join to become a part of God's organization here on earth the authority of it's civil laws no longer applied to those joining God's organization.
However, that does not set aside the 10 commandments as they were always covered by the mercy of God and speak to the condition of the human heart. They define sin. The civil laws defined a form of government. It was at this time that those laws were done away with in the written form given to the Hebrews.
However, the principles of the ten commandments still apply to all actions. Thou shalt not steal, thou shalt not covet, etc... still apply to us. They are part and parcel of love thy neighbor as theyself, and Jesus said that whoever does this fulfills the law. So, is it a sin for a Christian to loan out money at exhorbitant rates? Yes, for it is simply a civil government legalized form of theft. Is it a sin for us to borrow money? I believe it is if we are doing so at ridiculous rates. Why? Because God tells us that all we have and all we are belongs to Him. If we are paying out usurious interest rates we are robbing God of what is rightfully His and giving it to those who are in effect breaking God's law.
I guess everything I've said sort of boils down to, as long was we don't now violate the principles of Ten Commandments in our business practices that it isn't wrong, for civil law of the Hebrews is no longer our form of government.