Tefillah
The Midrash states that when Rivkah saw Yitzchak with his hands spread out in tefillah, she knew he was undoubtedly an adam gadol.
Once, people told the Satmar Rebbe about a person who is an adam gadol. The Satmar Rebbe asked them, "How do you know he is an adam gadol? Did you see him daven?" They asked him how the Rebbe knew that tefillah is the test of whether a person is an adam gadol. He answered them with the Midrash stated above. Rivkah saw the way Yitzchak was davening, and that is how she knew that he was an adam gadol.
When seeking a shidduch, someone asked the Chazon Ish, "How can I check whether the bachur has yiras Shamayim?" The Chazon Ish said that he should watch the bachur as he davens.
It states (Mishlei 27:21) מהללו לפי ואיש לזהב וכור לכסף מצרף, "The refining pot is for silver and the furnace for gold, and a man according to his praise." Hinted in these words is that a person can be tested to know who he is by how he praises Hashem.
The Beis Yisrael zt'l told this vort to his new gabbai. He wanted to tell him not to worry about coming late. If he is in the middle of davening, he should daven well, before coming to work to serve the Beis Yisrael.
The Baal HaTurim writes, "Eliezer sensed that they wanted to kill him, so he said that he wouldn’t eat before he speaks. I am Avraham's servant, and I trained myself in his house that I don't eat before saying the brachos of netilas yadayim and hamotzi. Eliezer thought that the brachos would send him blessings and save him... And that is what occurred; a malach came and switched his plate with Besuel’s, who ate the poison and died. Some say that Lavan and Besuel served him non-kosher food, and Eliezer told them דבר דברתי אם עד, I can't eat before I tell you something. אנכי אברהם עבד, I am Avraham's servant, and I don't eat non-kosher food.'"
It states (24:33-34) אכל לא ויאמר לאכל לפניו ויישם אנכי אברהם עבד ויאמר ,דבר ויאמר דברי דברתי אם עד, "[Food] was set before Eliezer to eat, but he said, 'I will not eat until I have spoken my words.' And he said, 'Speak.'"
The delay of this conversation saved Eliezer's life and enabled the shidduch to occur because Lavan and Besuel placed poison into Eliezer's food. As Eliezer was speaking, a malach came and exchanged the plates. Besuel died, and Eliezer survived.
The Imrei Emes zt'l says that דברי דברתי mentioned in the pasuk above alludes to tefillah. Eliezer told them that he couldn’t eat before he davened. Indeed, that is the halachah: one doesn't eat before davening. They told him, דבר, "So go daven," figuring that it won't take long. Eliezer replied, עבד אנכי אברהם, I am a servant of Avraham, and he taught us to daven with kavanah and without rushing through the words.
