Hi, Layane. Given that expression is used in a religious context, its meaning might be grasped under this light. In fact, 'walk' is probably used in a metaphorical manner, comparing a person's way of living to his or her way of walking. From this standpoint, the "walk" of someone "who compose[s] the house of God" is not too different from his or her "ways", which leads to the conclusion 'the walk and ways' can be understood as a whole in this case. The preposition 'in' is directly linked with 'exemplified', that is, it is used mainly because of this verb. It is similar like: 'something is reflected or shown IN a certain situation'. Based on these thoughts, I would translate the whole sentence the following way: "Isso demonstra que a verdade não apenas deve ser declarada de forma doutrinária nas atividades públicas, mas também deve se manifestar NA CAMINHADA daqueles que compõem a casa de Deus" I didn't translate 'public ministry' as 'ministério público' because this expression in Brazil refers to a state institution, namely the one where prosecutors are seated.

What you mean in English with it? Do you refer to the behaviour ("comportamento") of "those who compose the house of God" or to the way lead their lives (a forma como conduzem sua vidas)? 8-)

This is how I'd translate it: Isso mostra que a verdade não deve ser apenas descrita na doutrina em ministério, mas também deve ser exemplificada X na tajetória e nos caminhos X daqueles que compõe a casa de Deus. DISCLAIMER: this is a pretty literal translation, and I am not a translator. Thus, you can say something like this in ways that sound more natural, but are not exactly the same as was written here.