הלכה על שבת 238:5

Kaddish is unique in that it deals primarily with God’s honor (kevod Shamayim), and therefore, one’s response must be with intense kavana, and one certainly should not chatter during its recitation (SA 56:1; MB 1). The Sages say that anyone who answers “Amen, Yehei Shemei Rabba Mevorakh…” (“May His great name be blessed…”) with their full powers of concentration will cause a judgment of even seventy years against him to be torn up (Shabbat 119b; Talmidei Rabbeinu Yona). They further say that when Jews enter the synagogues and recite “Yehei shemei rabba mevorakh..” aloud, harsh decrees against them are nullified (Tosafot ad loc., citing Pesikta). Additionally, they say that the answer to Kaddish arouses mercy for Jews in exile. When Jews enter synagogues and batei midrashot and respond, “Yehei shemei rabba mevorakh…,” the memory of those in exile ascends before God, and He shakes His head in pain, so to speak, and says: “Fortunate is the king who was glorified this way in his house,” and the desire to redeem Israel awakens before Him (see Berakhot 3a).