This book of the law shall not depart out of thy mouth; but thou shalt meditate therein day and night, that thou mayest observe to do according to all that is written therein; for then thou shalt make thy way prosperous, and then thou shalt have good success.
The following statement from the Lord was given to Joshua before he led the Israelites to victory in the promise land. The book of the law mentioned in the scripture is the laws the Lord gave to Moses for the Israelites to follow and obey. The laws, or the Torah, is one of the books studied by the followers of Judaism.
The book of the law that the Christians study is known as the Bible. I describe it as the book of the covenant, which is an agreement with God (through Jesus Christ). In this book, it has the Old Testament (which has the Torah) and the New Testament (which has the gospels of Jesus Christ). As Christians, we acknowledge the laws of the Old Testament, but we are not in bondage to it (Galatians 2:19-21). We recognize that Jesus died for our sins on the cross. We are not made right by following the laws in the Torah, because we would all fail to meet the requirements of it. We are made right with God by believing in Christ and making a conscious effort to not sin. So, when we meditate, we meditate on the whole Bible, especially the gospels of Jesus Christ.
Only by doing this will God make us prosperous and successful in everything we do; by believing that Christ died for our sins. Like it says in 2 Corinthians 8:9, “For ye know the grace of our Lord Jesus Christ, that, though he was rich, yet for our sakes he became poor, that ye through his poverty might be rich.”