Rom 10:5-13, Deut 30:11-12, 14, Isa 28:16, Joel 2:32
In the Old Testament, God said that those who obey the law will live. (Deuteronomy 4:1)
Deuteronomy 4:1 Now therefore hearken, O Israel, unto the statutes and unto the judgments, which I teach you, for to do them, that ye may live, and go in and possess the land which the Lord God of your fathers giveth you.
The Old Testament says that if the law given by Moses is in our hearts, we will be able to obey it. (Deut 30:11-12,14)
Deut 30:11 For this commandment which I command thee this day, it is not hidden from thee, neither is it far off. 12 It is not in heaven, that thou shouldest say, Who shall go up for us to heaven, and bring it unto us, that we may hear it, and do it? 14 But the word is very nigh unto thee, in thy mouth, and in thy heart, that thou mayest do it.
The Old Testament says that man will live when he believes in Christ, the tested stone. (Isa 28:16)
Isa 28:16 Therefore thus saith the Lord God, Behold, I lay in Zion for a foundation a stone, a tried stone, a precious corner stone, a sure foundation: he that believeth shall not make haste.
The Old Testament says that those who call on the name of the Lord will be saved. (Joel 2:32)
Joel 2:32 And it shall come to pass, that whosoever shall call on the name of the Lord shall be delivered: for in mount Zion and in Jerusalem shall be deliverance, as the Lord hath said, and in the remnant whom the Lord shall call.
We are saved by believing in our hearts that Jesus is the Christ. (Romans 10:5-13)
Romans 10:5 For Moses describeth the righteousness which is of the law, That the man which doeth those things shall live by them. 6 But the righteousness which is of faith speaketh on this wise, Say not in thine heart, Who shall ascend into heaven? (that is, to bring Christ down from above:) 7 Or, Who shall descend into the deep? (that is, to bring up Christ again from the dead.) 8 But what saith it? The word is nigh thee, even in thy mouth, and in thy heart: that is, the word of faith, which we preach; 9 That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved. 10 For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation. 11 For the scripture saith, Whosoever believeth on him shall not be ashamed. 12 For there is no difference between the Jew and the Greek: for the same Lord over all is rich unto all that call upon him. 13 For whosoever shall call upon the name of the Lord shall be saved.