Galatians 1:6–7 (ESV)

6 I am astonished that you are so quickly deserting him who called you in the grace of Christ and are turning to a different gospel—  
7 not that there is another one, but there are some who trouble you and want to distort the gospel of Christ. (Emphasis Added)

We are called in the grace of Christ.

Paul refers to the grace of Christ as the gospel of Christ.

Acts 20:24 (ESV)

24 But I do not account my life of any value nor as precious to myself, if only I may finish my course and the ministry that I received from the Lord Jesus, to testify to the gospel of the grace of God. (Emphasis Added) 

The gospel and grace are used interchangeably in scripture. The gospel of Christ is the grace of God. And the gospel of grace is this: Jesus offered one sacrifice for sins forever; he died on the cross and took your sins past, present, and future. The gospel of grace is over the top good news that your sins have been done away with on the...