Keeping the Sabbath is one of the Ten Commandments. The Lord created the heavens and the earth in six days and rested on the seventh, so He made the Sabbath a holy day of rest.
Tithes were from the old covenant and commanded the Jews to give a tenth of their harvest and proceeds to the priests and Levites so they could devote themselves to the Law of the LORD. These were the spiritual leaders of the people. In addition, the best food stores went into storage so that if anyone had a shortage they could eat from the stock collected. So in addition to supporting the clergy the tithes went to supporting a social welfare system. Today the federal government inefficiently does much of what the church used to do. The new covenant does not command us to give a tenth, but to give what is needed to care for those in need. Tithing will not get you into Heaven nor will not tithing keep you from Heaven, but we all need to support the church and those around us who are in need. Since the Lord will return sevenfold anything given in His name, it is advantageous of us to be as generous as possible in supporting those who go out and spread the Gospel.