The Seventh Commandment continues to set out God’s vision for how we are to treat our neighbor and how we, as sinful beings, can live together in community. The legal definition of stealing is understood to be taking the property of another without permission or legal right and having no intention of returning it. Seems pretty straightforward. The Lord commands you to not take what is not yours. This includes little things like extra catsup packets and sugar as well as the big things (cars, laptops, etc.). Commandments Nine and Ten get into some additional specifics of what not to take (especially as it pertained to ancient cultures), but for now, we will focus on what “not stealing” means for the Lutheran. Not only are we not to steal, we are to help our neighbor “improve and protect” that which is his. Those who break this commandment can expect the same to be done unto them. Sound familiar? “In everything do to others as you would have them do to you; for this is the law and the prophets.” (Matthew 7:12)
From Luther’s Small Catechism
Q. What does this mean?
A. We should fear and love God that we may not take our neighbor's money or property, nor get them by false ware or dealing, but help him to improve and protect his property and business [that his means are preserved and his condition is improved].
Excerpt From Luther’s Large Catechism*
236] But reflect what you will gain when, having come into your own property and being set up in your home (to which God will help with all misfortunes), it [your perfidy] will bob up again and come home to you, and you will find that where you have cheated or done injury to the value of one mite, you will have to pay thirty again.
245] And, in short, if you steal much, depend upon it that again as much will be stolen from you; and lie who robs and acquires with violence and wrong will submit to one who shall deal after the same fashion with him. For God is master of this art, that since every one robs and steals from the other, He punishes one thief by means of another.
250] Let this suffice as an explanation of what stealing is, that it be not taken too narrowly, but made to extend as far as we have to do with our neighbors. And briefly, in a summary, as in the former commandments, it is herewith forbidden, in the first place, to do our neighbor any injury or wrong (in whatever manner supposable, by curtailing, forestalling, and withholding his possessions and property), or even to consent or allow such a thing, but to interpose and prevent it. 251] And, on the other hand, it is commanded that we advance and improve his possessions, and in case he suffers want, that we help, communicate, and lend both to friends and foes.
Large Catechism Text in the public domain. http://bookofconcord.org/lc-3-tencommandments.php