Today’s Gospel reading gives us St. Matthew’s account of the Transfiguration. To witness such an event must have been utterly breathtaking. St. Peter manages a response to what he sees and hears before him. Likewise, when we encounter the living God in a profound way, it provokes a response in us. We cannot encounter God and remain in our prior state. St. Peter also recognizes that it is good for him and the other disciples to be there. The frequent connotation of the word St. Matthew uses for 'good' in verse four is 'beautiful' or 'excellent in characteristic(s)'.
It might seem that God the Father offers a rebuke, for there are cases where we see St. Peter tending to get ahead (or outside) of himself, to say the least. Yet, I think what we see happening here on the mount of transfiguration is the loving Father telling St. Peter and us what the right response is when we encounter Him. We are to listen and follow Jesus. While it is the right general response to want to do something. However, that thing we may be inclined to do, even if it seems right to us, may not be what God wants. It is easy for us to get off-kilter. Here the Father tells us exactly what we must do. In response to His giving us grace and mercy, as we encounter Him in prayer, service, fasting, worship, and so forth, is to continue to follow Jesus. To listen attentively to what the Son says to us. To fervently emulate the example of the Son.