Do some verses teach that baptism is necessary for salvation?

Does Mark 16:16 teach that baptism is necessary for salvation?

In Acts 10:47, Peter commanded people to be baptized who had already received the gift of the Holy Spirit. According to Romans 8:9, those who have the Spirit are born of God (John 3:6), so the new birth is independent of baptism. Being "born of water and of the Spirit" (v. 5) therefore cannot refer to baptism. The Greek construction could be translated, "born of water, even the Spirit." This is consistent with John’s explanation of the Lord’s words in 7:39: rivers of living water symbolize the Spirit.

Further, the New Testament presupposes that obedience characterizes those who are saved (Romans 6:17; 1 Peter 1:14). Since in Acts 10 Peter commanded believers in Cornelius’ house to be baptized, we should rightly expect every believer to be baptized. Mark’s gospel emphasizes that actions substantiate truth (1:27; 16:20), therefore those who believe will demonstrate their faith by obedience.

A more cogent response, though, may come from observing that Mark 16:16 describes two classes of people: those who believe and are baptized; those who do not believe. A third possible classification, those who believe but are not baptized, is not mentioned. Some of the many passages stating that those who believe (with no mention of baptism) are saved include Acts 16:31; Romans 10:10; John 3:36; 5:24; 6:47; 20:31.

D. Oliver