Prefiguration means that a person or object or symbol that appeared early in time represents or stands for a person or object or symbol that came later in time. For Christians, the prophets of the Old Testament, such as Joseph or Moses, were prefigurations of their Savior, Jesus Christ, the central figure of the New Testament. In other words, the greatness and virtue of the prophets were only lesser signs or indications of the superior greatness and virtue that Jesus Christ would exhibit. Thus, in a sense, Christians believed that the appearance of the prophets was for the purpose of preparing the world for the arrival of Jesus Christ.
The idea of prefiguration plays a dominant role in "Sonnet 106." However, in this poem Shakespeare is not concerned with religious prefiguration. Rather, he is concerned with the prefiguration of beauty. Like several of the other earlier sonnets, the purpose of this one is to praise the beauty of the young man.
In the first quatrain the speaker is examining all of the literature ("the chronicle") of the past. The word chronicle here (in line 1) refers to non-fictional and fictional literature. But it especially refers to poetry about love. In this literature the speaker is particularly interested in reading the descriptions of the most beautiful ("fairest") people ("wights"),