“The Bible speaks of salvation being free (Romans 3:24; 6:23). Why do you insist that we must ‘do’ something (such as being baptized) in order to be saved? And in Mark 16:15 – 18, why is baptism required but not the signs?”
Your question is a good one and I am happy to answer it. Let’s start with the latter passage where Jesus is speaking to the apostles. . .
“And He said to them, ‘Go into all the world and preach the gospel to all creation. He who has believed and has been baptized shall be saved; but he who has disbelieved shall be condemned. These signs will accompany those who have believed: in My name they will cast out demons, they will speak with new tongues; they will pick up serpents, and if they drink any deadly poison, it will not hurt them; they will lay hands on the sick, and they will recover.'” (Mark 16:15 – 18; New American Standard Bible)
Notice that there cannot be a question about what Jesus required for salvation: “He who has believed and has been baptized shall be saved.” This is what the apostles were to preach. And that is what they DID preach (Acts 2:38; 8:12; 16:30 – 33; 18:8; 22:16; etc.). But what of the argument that baptism is a work and salvation is free? Let’s look back the other two passages. . .
“For all have sinned and fall short of the glory of God, being justified as a gift by His grace through the redemption which is in Christ Jesus . . . For the wages of sin is death, but the free gift of God is eternal life in Christ Jesus our Lord” (Romans 3:23, 24; Romans 6:23).
Salvation is certainly free. And there is not a thing we can do to earn it. It is a gift. But does that mean there is nothing for us to do in order to receive it? Is there no “work” required to receive this gift? Notice John 6:29, “Jesus answered and said to them, ‘This is the work of God, that you believe in Him whom He has sent.’”
If all “work” is ruled out, then faith is ruled out. The truth is that believing in the Christ as our Savior does not earn us salvation but it is necessary in order to receive His gift of salvation. The same thing is true with the act of baptism. Baptism doesn’t earn us salvation but it is necessary in order to receive His gift of salvation. As the apostle Paul puts it, “faith working through love” (Galatians 5:6a).
Why require belief and baptism (Mark 16:16) but not require “the signs” (verses 17, 18)? The answer to that is simple. “Believe” and “be baptized” are commanded by Christ. This is what we are to do. We cannot please Him without doing His will. But “the signs” were not commanded!
These signs were the results of the promise of the Lord to the apostles. “These signs” were not the work of humans but were the work of God, as promised. You cannot obey a promise. And besides all that, this promise was never given to all the believers. It was given only to the apostles, to enable them to “confirm the word”, which they were to preach (Mark 16:20).