Religion of the Heart
Christianity is a religion of the heart. This does not mean that Christianity is without commands, laws, or divine expectations. What does it mean? It means that it is up to the individual to practice it personally. That is, no one, other than the individual, is going to enforce it. 
In Hebrews 8:10, we read, “For this is the covenant that I will make with the house of Israel after those days, says the Lord: I will put My laws in their mind and write them on their hearts; and I will be their God, and they shall be My people.” This is a quotation from Jeremiah 31:33. God was telling the people of Jeremiah’s day that the system of law He gave through Moses was not going to be used in the future. Instead, God was going to have a system in which each person decided whether to follow Him or not. This system would not be enforced by the national authorities (as was done under the Law of Moses), but within the heart and mind of the individual—in other words, by their own free will. Essentially, it would be a system based upon faith.
In that way, this is the same system of religion practiced by Abraham—a system based on faith. That is why in Romans 4 Paul highlights the faith of Abraham as an example. He was not under the law of Moses. His religion was of the heart, freely practiced, based on faith. Romans 4:13 states, “For the promise that he would be the heir of the world was not to Abraham or to his seed through the law, but through the righteousness of faith.” In other words, to be a faithful Christian, the choice is yours.