Paul quoted Moses’ words from Deuteronomy, “Say not in thine heart, Who shall ascend into heaven? (that is, to bring Christ down from above) Or, Who shall descend into the deep? (that is, to bring up Christ again from the dead.) But what saith it? The word is nigh thee, even in thy mouth, and in thy heart” (Rom 10:6-8). After having given the First and Great Commandment, “Hear, O Israel: The LORD our God is one LORD: And thou shalt love the LORD thy God with all thine heart, and with all thy soul, and with all thy might” (Deu 6:4-5), Moses said the same thing several times: “If thou shalt say in thine heart” (7:17); “Thou shalt also consider in thine heart” (8:5); “And thou say in thine heart” (8:17); “Speak not thou in thine heart” (9:4); “there be not a thought in thy wicked heart, saying” (15:9); “And if thou say in thine heart” (18:21); “that he bless himself in his heart, saying” (29:19); “But the word is very nigh unto thee, in thy mouth, and in thy heart” (30:14). Loving God with all our hearts isn’t just what we say out of our mouths, but what we say to ourselves in our hearts, “in thy mouth, and in thy heart.”
Abraham learned the hard way to NOT laugh at God, “Then Abraham fell upon his face, and laughed, and said in his heart, Shall a child be born unto him that is an hundred years old? and shall Sarah, that is ninety years old, bear? And Abraham said unto God, O that Ishmael might live before thee! And God said, Sarah thy wife shall bear thee a son indeed; and thou shalt call his name Isaac [laughter]” (Gen 17:17-19). Telling Abraham to name his son “laughter” indicated that God knew he had just laughed at Him in his heart. Abraham got the point.
Jesus and John the baptizer both taught: “And think not to say within yourselves” (Mat 3:9); “But and if that evil servant shall say in his heart” (Mat 24:48); “and begin not to say within yourselves” (Luk 3:8); “he spake within himself, saying” (Luk 7:39); “And he thought within himself, saying” (Luk 12:17); “But and if that servant say in his heart” (Luk 12:45); “but afterward he said within himself” (Luk 18:4); “Then the steward said within himself” (Luk 16:3). We all speak to ourselves in our hearts. And since people don’t know what we’re saying, it’s very easy to forget that God does and begin speaking to ourselves evil things.
Jesus didn’t just suggest but commanded us, “Take no thought for your life, what ye shall eat, or what ye shall drink; nor yet for your body, what ye shall put on … take no thought, saying, What shall we eat? or, What shall we drink? or, Wherewithal shall we be clothed? … Take therefore no thought for the morrow” (Mat 6:25,31,34). We can’t be saved if we’re sinning against Christ’s commandment by thinking to ourselves about tomorrow. To take no thought for tomorrow requires that we trust God—that He becomes the God of our lives: “I will be their God” (Gen 17:8; Jer 24:7,32:38; Eze 11:20,36:28,37:23,27; Zec 8:8), “I will be their God” (2Co 6:16); “I will be to them a God” (Heb 8:10); “God is not ashamed to be called their God” (Heb 11:16); “God himself shall be with them, and be their God” (Rev 21:3); “I will be his God” (Rev 21:7). For God to be our Savior, God must be our God. It means no longer running our lives and ruining our lives!
“Trust in the LORD with all thine heart; and lean not unto thine own understanding” (Pro 3:5), requires that we don’t say anything to ourselves displeasing to God, try to figure out situations, or “help” God work things out. It means being truly at peace with any outcome and sincerely content in any circumstance we find ourselves, “I have learned, in whatsoever state I am, therewith to be content” (Phl 4:11). And this isn’t just a better way to live—it’s the way we must live to be saved.
The Greek verb pisteuō appears about 250 times in the New Testament and is almost always translated as “believe” but actually means “trust.” Paul taught about salvation, “That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe [trust] in thine heart that God hath raised him from the dead, thou shalt be saved. For with the heart man believeth [trusts] unto righteousness; and with the mouth confession is made unto salvation. For the scripture saith, Whosoever believeth [trusts] on him shall not be ashamed.” (Rom 10:9-11). That salvation isn’t by believing but by trusting is evident by what David said, “O my God, I trust in thee: let me not be ashamed, let not mine enemies triumph over me … O keep my soul, and deliver me: let me not be ashamed; for I put my trust in thee” (Psa 25:2,20), “In thee, O LORD, do I put my trust; let me never be ashamed” (Psa 31:1). Salvation isn’t by believing but by trusting God. Our trust in Him won’t be put to shame, “Whosoever believeth [trusts] on him shall not be ashamed.”
Paul understood Moses’ words “Say not in thine heart … in thy mouth, and in thy heart,” that we confess the Lord publicly out of our mouths, and speak trust in God privately within our hearts. To be saved, we must trust the Father and obey His Son.