A story once occurred at a festive gathering to celebrate the tenayim of a new chosson and kallah. All of the guests were sitting and waiting for the tenayim to be read when suddenly the father of the bride refused to sign on the document that obligated him to pay his daughter’s dowry. He claimed that he should be believed based on his word, as he was the type of person who never said a lie and, in any case, no one would lie about their own child. Therefore, he should be trusted without the need for a signed contract.
Amongst those in attendance was Rav Elchonon Wasserman zt”l. When he saw that the father was stubbornly insisting and that this could place the entire shidduch in danger, he spoke up and said to the man, “Your claim is incorrect. You say that no one would lie about their own child but this is not true. The proof of this is that during the Aseres Yemei Teshuva, we tell Hashem: ‘Remember me for life, oh King who desires life.’ We are Hashem’s children and we trust in Him to grant us life. So why do we then say ‘and write us in the book of life’? Why can’t we rely on Him without making Him write it down?’ We see from here that a promise is not sufficient unless it is in writing!”
Rav Moshe Londinsky zt”l, Rosh Yeshivas Radin, added that even a written promise is not as good as something given from hand-to-hand. This is seen from the bikkurim. When one goes to his field and sees the first fruits, he ties them with a reed and later puts them in a basket and he takes them to Yerushalaim. After all of this, one certainly can assume that he will fulfill his pledge and give them to the kohen.
Still and all, the Torah says that he must give them to the hand of the kohen, and the kohen must take the basket from him. Why is this necessary? Because one cannot be 100% sure that the bikkurim will be given until the kohen takes it.
