From the Lamb's Supper by Scott Hahn Pg. 156

From the moment you walk into church, you place yourself under oath. By dipping your fingers into holy water you renew the covenant begun with your baptism. Perhaps you were baptized as an infant; your parents made the decision for you. But now, with this simple motion, you make the decision for yourself. You touch the water to your forehead, your heart , and your shoulders and you sign yourself by "the name" in which you were baptized/Wrapped up in this motion is your acceptance of the creed, which your parents accepted in your name at your baptism. Wrapped up in this motion is your rejection of Satan, and all his pomps and all his works.

Doing this you testify, you make testimony, as you would in court. In court a witness puts himself, his reputation and his future on the line. If he fails to tel the truth, the whole truth, and nothing but the truth, he knows he will face severe consequences.

You, too, are under oath. When you make the sign the sign of the corss you renew the sacrament of baptism, thus renewing your obligation to live up to the rights and duties of the New Covenant. You will lvove God with all your heart and mind and sould and strength, you will love your neighbor as yours"Amen" The Aramaic word that conveys assent and agreement
Yes! ! "Amen" is more than a response it is a personal commitment when you say "Amen" you commit your life.

Thus in the Mass, you are not merely a spectator, your are a participant. Yours is the covenant that you will renew. Yours is the covenant that Jesus Himself will renew here and now.