When there are differing views over something like baptism by very scholarly theologians, how can the lay person know which interpretation is correct? Thank you.
What can be helpful is keeping in mind how “scholarly theologians” might view the Bible in the first place. This link will take you to a “Light for our path” column that explains how many theologians today approach Scripture.
With that background in place, if “scholars” have their minds made up what baptism is and is not, they will look to Scripture to find support for their views. That, of course, is completely backwards from how we are to read the Bible. We are to read the Bible and come away with the truths that God has expressed.
Many “scholarly theologians” read the Bible through the lens of human reason. If words of Scripture do not make sense to them, they inject a meaning that is sensible to them. So, for example, since some people believe that they are responsible for Christian faith, they reject infant baptism. In addition to a denial of original sin, their line of thinking is that an infant does not possess the intellectual abilities to comprehend what is going on in baptism, and so they are not in a position to make a decision for Christ.
When we understand that Christian faith is a gift from God (Ephesians 2:8), then we will recognize that God can give that gift to young and old alike through his gospel in word and sacrament. And then, we will not put limitations on the great commission (Matthew 28:19-20)—baptizing only adults.
So, what are you to think when “scholarly theologians” reach wildly different conclusions on what the Bible says? I would encourage you to read the Bible for yourself and follow the principle of letting “Scripture interpret Scripture.”
Don’t downplay your role as a Bible interpreter compared to “scholarly theologians.” Martin Luther’s well-known observation about laity and theologians was this: “A simple layman armed with Scripture is to be believed above a pope or a council without it.” That goes for a simple professor too.