J.I. Packer has said that baptism is a secondary doctrine that should not separate evangelicals. I think that he is right in terms of his own parameters. Evangelicals have an unbiblical view of baptism, denying its efficacy to remove sins, and so, whether they practice covenant baptism or baptistic submersion, they are really on the same hymn sheet.
Evangelism is central to evangelicalism, and central to evangelism is the so-called conversion moment where an unbeliever makes a decision for Christ, or says the sinners’ prayer, or whatever particular thing it is that they call for. Baptism has no connexion to this alleged conversion moment at all, according to the universal agreement of evangelical theology.
The Bible says otherwise on so many words. The prophets and apostles teach us in plain words that baptism is for the remission of sins and the gift of the Holy Spirit. The texts are so plain that disagreement cannot be permitted, because there is no common middle ground. That baptism is for the remission of sins means that the evangelical model of conversion is wrong, un-Christian, and unbiblical.
Most people are converted when they are baptised. Period. Baptism is the conversion experience of the overwhelming majority of believers, with very few exceptions.
There are cases where baptised unbelievers come to faith, no question about it. In many instances these are men who were brought to Christ at the font, and then spiritually abandoned by their parents. They were not taught the faith, the commandments, or prayer. They were plants left unwatered, and so their faith perished.
Later in life someone poured the water of the gospel into their ears, and the seed that was implanted in them by their baptism sprang back to life, and their baptism was completed and improved.
Conversions of unbaptised men are more rare, in my experience, and in the experience of the wider church. By far the majority of church-goers are the children of church-goers. Where we need to do more thinking and reading is learning how to bring baptised unbelievers back to their ancestral faith.
In closing, then, baptism is central to the gospel, not secondary. There is no room for disagreement here. This position was shared by all the Reformers, Fathers, and Presbyterian and Continental Confessions – with no exceptions.