The Old Testament Law points out our sin. Breaking the Law = Sin.

God sacrificing His only Son (Jesus) on the cross as a full payment for our sins = Grace/Gospel.

Those who rely on strict adherence to the rules of the Law of God are known as "legalists". They strive hard to follow every step of every command and feel if they make a mistake they have failed miserably. 

Those who rely on the amazing grace of God's gospel as a reason to freely sin without moral restraint are known as a "licentious" Christian. They don't want to be bound by the suffocating rules of the Law because living like that is boring and lacks adventure and joy. 

Leaning heavily one way or the other is probably an unhealthy approach to Christian living. 

No human is perfect and able to have no sin in their lives except for Jesus Christ. So being a legalist is hard. And living a wild life of sin, while ignoring the Law because God has saved you is not pleasing to God. Look what Paul says in the book of Romans chapter 6: "Shall we go on sinning so that grace may increase? By no means! We are those who have died to sin; how can we live in it any longer?"

The mission is to accept Christ as your Savior, thus welcoming the Holy Spirit in your life. In doing so, you have salvation for eternity and forgiveness for your sins, AND you have the power to wake up and attempt very hard to follow God's holy commands and Law. And do it with gladness and joy, not looking at the Law and commands as a punishment or a "boring/bad way" to live life. Instead see it as a joy that God has given us instructions on how to live in a manner that is good for us and glorifies Him.

 Delight and give thanks to God for saving you while also giving God thanks for establishing His law and wanting us to gladly strive to live a life worthy of His calling.