Parshas Lech Lecha presents us with the unfolding of Jewish history. Avraham is the first Jew, not the first monotheist. The greatness of Avraham as told to us in Bereishis (18:19) is his capacity to transmit his values and beliefs to subsequent generations, something that his great predecessors including Chanoch, Noach, Shem, and Ever were not able to do.
The Mishna in Avos (5:4) teaches that, "Asarah nisyonos nisnasa avraham avinu veamad bekulam, lehodiya kamah chibaso shel avraham avinu." Our forefather Avraham was tested with ten trials and he withstood them all, to show the degree of our forefather Avraham's love for God. Although there are different ways to reckon the exact nature of the ten tests, according to the Bartenura, seven of these tests are found in Parshas Lech Lecha.
What is the purpose of a test? It is clearly for man, as Hashem knows if man will pass the test or not. The Ohr HaChaim in his commentary on Bereishis (3:4,5) asks why Hashem tested the first couple with the snake? The Ohr HaChaim posits the thesis that ultimately it is in man's best interest to be challenged, and pass the test. Moreover, the reward received is commensurate with the energies expended in passing the test, as we are taught in Avos (5:23) "Lefum tzaara agra "- commensurate with the pain/difficulty and struggle is the gain and personal reward. The very term "nisayon" (test or trial) comes from "ness" (banner). Each triumph over a test elevates the individual. Without the test there is no personal advancement or growth.
Avraham was not born "Avraham Avinu"- our father, rather he developed and matured his relationship with Hashem by successfully overcoming his natural instincts and living a life dedicated to higher ideals. The Torah teaches us in Bereishis (15:5) that Hashem took Avraham outside to count the stars and say to him "koh yehiye zaracha" - Thus shall be your seed. In addition to the literal interpretation that his offspring would be as numerous as the stars, Rashi cites the medrash which teaches that Hashem removed Avraham from the natural circumstances of this world and informed him that Avram would not have a son but Avraham would; Hashem would change his name and his destiny. Rashi (17:1) explains the significance of adding the letter hey to Avram's name as signifying Avraham's ability to control and master morally five organs (eyes, ears, and procreation). Avram grows into Avraham. Rav Chaim Yaakov Goldwicht zt"l, founding Rosh Yeshiva of Yeshivas Kerem B'yavne, explains that the pasuk "koh yehiye zaracha" - "Thus shall be your seed" - can be interpreted as saying that so to will your children possess the ability to rise above their challenges and pass their tests. This may be seen from the Medrash Braishis Rabbah (87:8) that attributes Yosef's ability to "flee and run outside" (Braishis 39:15) and pass his test to the merit of his great-grandfather Avraham, regarding whom we are told similarly, "vayotse oso ha'chutsa" - "Hashem brought him outside".
The Gemara Sanhedrin (107a) teaches in the name of R. Yehuda in the name of Rav, "a person should never bring himself to a test", i.e., should not intentionally place himself into a situation in which he will be tested to sin, for King David brought himself to a test and stumbled and succumbed to temptation. David asked Hashem why could he not be included in the opening blessing of the Shemoneh Esray, and amend the blessing to read, "God of Avraham, God of Issac, God of Jacob, and God of David". Hashem answered that the three patriarchs were tested by Him and withstood the tests, whereas David had not been tested. David then asked to be tested. Hashem agreed and even told him that the test would be in the area of physical temptation. Though forewarned, that night David sinned with Bat-Sheva.
It is true that every morning we pray "do not bring us into the power of error, nor into the power of transgression and sin, nor into the power of challenge", as we are fearful that we will not pass the test. Rav Chaim Shmulevitz zt"l in his Sichos Mussar (5733:6) explains that when Hashem tests an individual, He provides them as well with the ability to withstand the test. Hashem only tests those that can pass. However, when one brings a test upon himself, he is not necessarily awarded the divine assistance needed to pass the test.
We conclude the Hallel with "o'dcha ki anisani" - "I thank you Hashem for answering me". The Malbim understands this to mean, I thank you for the challenges and difficulties you have placed before me, cognizant, as the Ohr Hachayim teaches, that "the greater the physical and spiritual effort to overcome potential impediments to our faith, the greater the reward stored up in Heaven for such acts of faith".