Rebuked, Rebuker
Acts 8:19-20
Now when Simon (the "magician") saw that the Spirit was given through the laying on of the apostles' hands, he offered them money, saying, "Give me this power also, so that anyone on whom I lay my hands may receive the Holy Spirit." 
But Peter (Cephas) said to him, "May your silver perish with you, because you thought you could obtain the gift of God with money! You have neither part nor lot in this matter, for your heart is not right before God."

Galatians 2:11-16
When Cephas (Peter) came to Antioch, I opposed him to his face, because he stood condemned.
For before certain men came from James, he was eating with the Gentiles; but when they came he drew back and separated himself, fearing the circumcision party. And the rest of the Jews acted hypocritically along with him...But when I saw that their conduct was not in step with the truth of the gospel, I said to Cephas (Peter) before them all, "...We know that a person is not justified by works of the law but through faith in Jesus Christ, so we also have believed in Christ Jesus, in order to be justified by faith in Christ and not by works of the law, because by works of the law no one will be justified."

In Acts 8, Peter rebukes a fellow named Simon who thinks that God's grace can be got with money. In Galatians 2, Paul rebukes Peter for thinking that God's grace can be got with works.

See how quickly the rebuker becomes the rebuked.

See how quickly we turn from defending the free grace of the Gospel, to hedging our bets against the worry, "What if Jesus and His work aren't not enough..."

Just because you know the Gospel, just because you saw Jesus in His glory, just because you saw His body on the tree, just because you touched the place where He lay, just because you talked with Him and saw Him ascend to the Father, just because you saw the Spirit fall like fire on the disciples, just because you were so anointed by the Spirit that your shadow would heal the sick, just because you stood firm for the grace of the Gospel of God over and over again.

Don't think you're heart loves the Gospel best of all, always and forever.

Hear the Christmas news: the Gift of God is free. It cannot be bought. It cannot be earned. It is not deserved. What you have in Christ, you have freely or not at all. 

Rejoice in the grace of God! Tremble at our bent to "nullify the grace of God." (Gal 2:21)

It's grace or nothing, for sinners like us. Thanks be to God! It's grace!