Why does Rashi explain that the declaration that one makes when one brings the first fruits should be made in a loud voice?
(26,5) “And you shall call out and say before Hashem, your G-d: An Aramean sought to destroy my forefather…”
Rashi explains that the expression “you shall call out” means with a loud voice. What does Rashi wish to teach us?
The answer is that the gemora in Berachos 31a teaches that it is forbidden to raise one“s voice when one prays because that makes him seem like one who is lacking in faith since it implies that he thinks that Hashem will not answer a quiet prayer and that He is unable to examine the heart and mind of a person, G-d forbid. According to this, if a person states in his prayer something from which it is clear to everybody that Hashem examines the hearts and knows the minds of people, then it would be permissible to pray in a loud voice.
Therefore, since the one who brings the first fruit states that “an Aramean sought to destroy my forefather” - that Lavan had considered in his thoughts to uproot the Jewish nation but Hashem saved us from him because He knew his thoughts and what was in his heart, in this case it is permissible to raise one’s voice.
This is what Rashi is coming to teach with his explanation that “and you shall call out” means with a loud voice. But how can Rashi say this? Surely it is forbidden to raise one’s voice when praying! But the posuk continues that the person states that “an Aramean sought to destroy my forefather” in his thoughts, and therefore it is permissible here to raise one’s voice.