VIII. The Father's words have a universal application to the whole Church
These things, dearly-beloved, were said not for their profit only, who heard them with their own ears, but in these three Apostles the whole Church has learned all that their eyes saw and their ears heard. Let all men's faith then be established, according to the preaching of the most holy Gospel, and let no one be ashamed of Christ's cross, through which the world was redeemed. And let not any one fear to suffer for righteousness' sake, or doubt of the fulfilment of the promises, for this reason, that through toil we pass to rest and through death to life; since all the weakness of our humility was assumed by Him, in Whom, if we abide in the acknowledgment and love of Him, we conquer as He conquered, and receive what he promised, because, whether to the performance of His commands or to the endurance of adversities, the Father's fore-announcing voice should always be sounding in our ears, saying, “This is My beloved Son, in Whom I am well pleased; hear Him:” Who lives and reigns, with the Father and the Holy Ghost, for ever and ever. Amen.
Source: Sermons (New Advent)