And if you are Christ's, then you are Abraham's offspring, heirs according to promise. - Galatians 3:29
In Jesus Christ, you have every promise of God. You are an heir to all God has for you.
The heir of royalty did nothing to be an heir. When they are born, they were born into the royal family. Their birth made them an heir. Because they were born into the family, all the blessings, wealth, and privilege of the family are theirs.
So many Christians want to add things to the Gospel. They say you need Jesus and something else. You need Jesus and follow this or that set of rules. In the Apostle Paul's day, there were those who thought you needed Jesus and the law of Moses. They thought to be a real Christian, required faith in Christ, and following the traditions and law of the Jews.