Avraham and Emunah
וְהִנֵּ֨ה דְבַר־יְהֹוָ֤ה אֵלָיו֙ לֵאמֹ֔ר לֹ֥א יִֽירָשְׁךָ֖ זֶ֑ה כִּי־אִם֙ אֲשֶׁ֣ר יֵצֵ֣א מִמֵּעֶ֔יךָ ה֖וּא יִֽירָשֶֽׁךָ׃
The word of יהוה came to him in reply, “That one shall not be your heir; none but your very own issue shall be your heir.”
וַיּוֹצֵ֨א אֹת֜וֹ הַח֗וּצָה וַיֹּ֙אמֶר֙ הַבֶּט־נָ֣א הַשָּׁמַ֗יְמָה וּסְפֹר֙ הַכּ֣וֹכָבִ֔ים אִם־תּוּכַ֖ל לִסְפֹּ֣ר אֹתָ֑ם וַיֹּ֣אמֶר ל֔וֹ כֹּ֥ה יִהְיֶ֖ה זַרְעֶֽךָ׃
[Then in the vision, God] took him outside and said, “Look toward heaven and count the stars, if you are able to count them”—continuing, “So shall your offspring be.”
וְהֶאֱמִ֖ן בַּֽיהֹוָ֑ה וַיַּחְשְׁבֶ֥הָ לּ֖וֹ צְדָקָֽה׃
And he put his trust in יהוה, who reckoned it to his merit.

והאמן בה' ויחשבה לו צדקה פירש רש"י (רש"י על בראשית ט״ו:ו׳) הקדוש ברוך הוא חשב לו צדקה וזכות על האמונה שהאמין בו ואיני מבין מה הזכות הזאת למה לא יאמין באלהי אמן והוא הנביא בעצמו ולא איש אל ויכזב ומי שהאמין לשחוט את בנו היחיד האהוב ושאר הנסיונות איך לא יאמין בבשורה טובה

AND HE BELIEVED IN THE ETERNAL; AND HE ACCOUNTED IT TO HIM FOR RIGHTEOUSNESS. Rashi’s explanation is: The Holy One, blessed be He, accounted it to Abraham for righteousness and merit because of the faith with which he had trusted in Him.
But I do not understand the nature of this merit. Why should he not believe in the G-d of truth, and he himself is the prophet, and G-d is not a man, that He should lie? Furthermore, he who believed [and on the basis of this belief was ready] to sacrifice his only son, the beloved one, and withstood the rest of the trials, how could he not believe a good tiding?

וַיֹּ֣אמֶר יְהֹוָה֮ אֶל־מֹשֶׁ֣ה וְאֶֽל־אַהֲרֹן֒ יַ֚עַן לֹא־הֶאֱמַנְתֶּ֣ם בִּ֔י לְהַ֨קְדִּישֵׁ֔נִי לְעֵינֵ֖י בְּנֵ֣י יִשְׂרָאֵ֑ל לָכֵ֗ן לֹ֤א תָבִ֙יאוּ֙ אֶת־הַקָּהָ֣ל הַזֶּ֔ה אֶל־הָאָ֖רֶץ אֲשֶׁר־נָתַ֥תִּי לָהֶֽם׃
But יהוה said to Moses and Aaron, “Because you did not trust Me enough to affirm My sanctity in the sight of the Israelite people, therefore you shall not lead this congregation into the land that I have given them.”