When Avraham was already an elderly man, he received the long awaited tiding that he would bear children. The Torah tells us, "He believed in Hashem and He reckoned it to him as righteousness" (Bereishis 15:6). Rashi explains that the fact that he believed that he would bear children was a merit. The Ramban contends that there must be a different explanation because Avraham heard a prophecy directly from Hashem to this end, so what was so great about the fact that He believed what he heard straight from G-d? The Maharal counters that perfect belief isn't so simple because we find that even Moshe was taken to task after hitting the rock as the pasuk tells us, "Because you did not believe in Me to sanctify Me before the nation..." (Bamidbar 20:12). In light of this, Avraham's total belief was indeed meritorious.
Rav Wolbe (Shiurei Chumash, Noach 7:7, Alei Shur vol. II pg. 338) elaborates that there are many levels of emunah. While we might refer to emunah simply as believing that there is a Creator, this is only the most basic level of emunah. The Torah is discussing a much greater level of emunah. Avraham believed in Hashem that he would bear children when all of nature belied such a possibility. He and his wife were well past their childbearing years, and moreover, Chazal tell us that Sarah did not even have the physical organs needed to bear children! The scientific impossibility did not sway Avraham even an iota from complete faith in what he was told.
In contrast, in Parshas Noach we read how Noach was forced into the teivah by the rainwater heralding the beginning of the deluge. Rashi (Bereishis 7:7) comments that Noach was lacking in emunah. He did not believe with full certainty that the flood would come, and consequently, he did not enter the teivah until the intensity of the rains precluded the possibility of him staying outside. He, too, had received his information regarding the future via a prophecy directly from Hashem. Nevertheless, he needed to experience something tangible in order to truly believe that the prophecy would come to fruition.
One who possesses total belief in Hashem's word, believes in everything Hashem said even if he has not heard the prophecy himself. His belief is so ironclad that he is even willing to put his life on the line should the need arise. The Gemara (Gittin 56b) relates that during the siege of Yerushalayim just prior to the destruction of the second Bais Hamikdosh, R' Yochanan ben Zakkai arranged a secret meeting between himself and the Roman general Vespasian. As they met, he extended his greetings, "Peace unto you, king." Vespasian replied that such a greeting warrants the death penalty because it implied that he had rebelled against the reigning emperor and wished to coronate Vespasian in his stead! R' Yochanan replied that indeed he must be a king, because Chazal inferred from a pasuk that the Bais Hamikdosh would be destroyed only by a king. (Immediately thereafter, a messenger arrived from Rome with the news that the emperor had died and the higher echelons in the Roman government decided to coronate Vespasian as his successor!) The fact that R' Yochanan saw a general in front of him did not influence his behavior in any fashion. He was willing to valiantly address Vespasian as king; knowing that had he erred, his mistake would be fatal.
This idea has many practical applications for every one of us, and is especially relevant in light of the terror attacks in Israel. Earlier in this week's parsha, after the war with the four kings, we read how Avraham agreed to accept payment for the food eaten by the soldiers who fought the war and those who sat watching the vessels. Rashi infers that those who fought in battle and those who manned the base received equal portions of the spoils. Accordingly, David Hamelech would apportion the spoils of the battles that he fought, in a similar fashion.
Why do they both deserve the same amount of booty? Doesn't the soldier fighting the war deserve more than those sitting effortlessly at the base? Rav Wolbe (Shiurei Chumash, Lech Lecha 14:24) cites the meforshim in Shmuel (I, 30:24) who explain that soldiers only deserve more if they are fighting a "natural" war. However, when wars are fought by Hashem, it makes no difference who puts in more or less effort, so long as each person is doing what is incumbent upon him to do. Thus, while the soldiers are the ones holding the weapons, it is us who have the ability to bring them (and all the civilians) home safely each night. If our emunah would be concrete and we genuinely believed that, although it appears as if the guns decide the outcome, the truth is that our Torah and tefillah call the shots, then our prayers would be with an intensity that rivals the intensity of a soldier in battle!