The human writer of the book of Acts is believed to be Luke. It continues from where he left off in the Gospel of Luke. An amazing feature of the Bible is that one part of it is always in agreement with other parts of it.
Here we see that he is in perfect agreement with Christ, the Apostle Paul, and others about salvation being entirely by grace. The reason that salvation is by grace is because "ye could not be justified by the law of Moses."
All the law can do is to condemn. If you break it, you pay the penalty. That is the way it is with all laws. Keeping laws are not a "get-out-of-jail" card when you have broken one. Just because you have kept the speeding laws for 364 days a year and then get a speeding ticket does not mean that you will not need to pay the fine for breaking it on one day. Your good driving record does not erase the bad record when you stand before the judge.
The same is true with salvation. Because the law can only condemn, salvation must come another way. Christ paid the full price for our sin. The way to take advantage of the price is to admit you are a sinner to God, and to ask Jesus Christ to become your Savior - believing that He will do what He said.
Did you notice what the first part of the verse said? It said: "And by him (Christ) all that believe are justified from all things." It means just what it says. There is no sin that is not forgivable in God's eyes – if you will believe that Jesus died for your sins. He invites you to come as you are and let Him forgive, cleanse you, and save you. He wants to do all the work. This way He gets all the glory.
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Keywords: justified, believe, Christ, Jesus, sins, forgive, save, law, grace