What is perhaps the key distinction between these two notions is that, traditionally, theology spoke strictly of orthodoxy (correct beliefs), whereas Gutierrez maintains that orthodoxy and orthopraxis (correct practices) have a mutually dependent relationship, where each helps to define the other.
To believe (life) and to understand (reflection) are always part of a circular relationship … orthopraxis and orthodoxy need one another, and each is adversely affected when sight is lost of the other.
Most of the famous theologians sought to understand God through the application of reason (rational knowledge) based on the Bible (wisdom). It worked to create a consistent picture of who God is, how he works, and how we should respond. While it no doubt had a spiritual element for many, it was, primarily, a mental practice.
Gutierrez, on the other hand, put less emphasis on trying to make sense of God through reason and instead argued that an integral part of knowing God is reflecting on the actions of Jesus and those who knew him personally—specifically, the early church.
These early Christians did not spend their time locked away in monasteries, trying to deduce God's nature. Rather, they understood God by doing his work--namely, by ministering to the poor and oppressed. And this, for Gutierrez, is the principle first act of Christianity, and must be the lens through which all other Christian theology is understood.
To that end, the "critical reflection" is understanding Christianity the way he believes it was meant to be, through living God's word like those of the early church, rather than just studying it.
In short, the traditional idea of theology was that faith came first, and then understanding (through reason) afterward. Gutierrez, instead, argues:
All this means that the life of faith is not only a starting point, it is also the goal of theological reflection.