Though not explicitly about the Trinity, the below quote from Sanders’s The Deep Things of God: How the Trinity Changes Everything was one of the most impactful for me. Up until fairly recently, I was the kind of reductionistic evangelical described below. Probably largely as a subconscious response to the Christless/cross-less moralistic/deistic “Christianity” so popular in American evangelicalism, my theology was all about the cross. And I didn’t realize for a time that if you’re only about the cross, your faith is actually anemic, not robust and healthy like you might think. Sanders puts it well. Conservative evangelicals, take heed.
Bible, cross, conversion, heaven. These are the right things to emphasize. But in order to emphasize anything, you must presuppose a larger body of truth to select from. For example, the cross of Christ occupies its central role in salvation history precisely because it has Christ’s preexistence, incarnation, and earthly ministry on one side and his resurrection and ascension on the other. Without these, Christ’s work on the cross would not accomplish our salvation. But flanked by them, it is the cross that needs to be the focus of attention in order to explain the gospel. The same could be said for the Bible within the total field of revelation, for conversion within the realm of religious experience, and for heaven as one of the benefits of being in Christ. Each of these is the right strategic emphasis but only stands out properly when it has something to stand out from.
When evangelicalism wanes into an anemic condition, as it sadly has in recent decades, it happens in this way: the points of emphasis are isolated from the main body of Christian truth and handled as if they are the whole story rather than the key points. Instead of teaching the full counsel of God (incarnation, ministry of healing and teaching, crucifixion, resurrection, ascension, and second coming), anemic evangelicalism simply shouts its one point of emphasis louder and louder (the cross! the cross! the cross!). But in isolation from the total matrix of Christian truth, the cross doesn’t make the right kind of sense. A message about nothing but the cross is not emphatic. It is reductionist. The rest of the matrix matters: the death of Jesus is salvation partly because of the life he lived before it, and certainly because of the new life he lived after it, and above all because of the eternal background in which he is the eternal Son of the eternal Father. You do not need to say all of those things at all times, but you need to have a felt sense of their force behind the things you do say. When that felt sense is not present, or is not somehow communicated to the next generation, emphatic evangelicalism becomes reductionist evangelicalism.
Fred Sanders. The Deep Things of God: How the Trinity Changes Everything (Wheaton, IL: Crossway, 2010), 15-16.