QUESTIONS: How did the Old Testament people express their faith in the LORD? How are believers or Christians today supposed to express their faith in the LORD? Have the standards changed?
ANSWER: Those are excellent questions. The short answer is that God's moral standard is eternal. It doesn't change, because it reflects the character of our changeless God. And as a general principle, faith is expressed to God--before the cross, and after--by obedience to His Word. As the Bible says, "By faith Abraham obeyed" (Heb. 11:8).
Contrast that with what is said of Israel, poised to go in and conquer the Land of Canaan at God's command: "Likewise, when the LORD sent you from Kadesh Barnea, saying, ‘Go up and possess the land which I have given you,’ then you rebelled against the commandment of the LORD your God, and you did not believe Him nor obey His voice" (Deut. 9:23).
Take that link between faith and obedience as a basic starting point, and I think you'll see an answer to your questions. Whatever the specifics revealed for a particular time, that was to be the response. If Adam and Eve had fully believed and trusted God, they would have obeyed His command not to eat of the forbidden fruit (Gen. 2:17).
As far as the practical details of what's to be believed and obeyed, people can only act on what they know. By faith Noah believed God about the coming deluge, and so he obeyed the Lord's command and built the ark (Heb. 11:7). But these early saints didn't know about Christ, and what He would do on Calvary--or saw these things off in the future only very dimly.
At that stage of things we have God's commands regarding animal sacrifices. We know that an animal cannot die for the sins of a man (Heb. 10:4). It took "the Man Christ Jesus" to do that. However, God accepted the sacrifices of the Old Testament, when they were offered in faith, recognizing them as foreshadowing what was still unknown.
"He [the offerer] shall put his hand on the head of the burnt offering, and it will be accepted on his behalf to make atonement for him" (Lev. 1:4). This physical action was a means of identification with the sacrifice. It said, "This is an innocent substitute, dying in my place." And you can see that's exactly what we testify to when we put our faith in the Saviour, the "Lamb of God" (Jn. 1:29). He is the final and full Innocent Substitute (I Cor. 15:3; Eph. 1:7; I Pet. 3:18).
God's revelation was progressive. That is, more and more information was added as time went on. Not that the latter parts contradict what came earlier--certainly not in principle. But we now have God's full written revelation, and that places a greater responsibility upon us than believers of an earlier time.
Part of that increased responsibility is due to the fact that Christ has come to earth as Man, revealing God to us in a way we can more fully understand (Jn. 1:14). And in the process God revealed the true standard for man in His Son. "God, who at various times and in various ways spoke in time past to the fathers by the prophets, has in these last days spoken to us by His Son" (Heb. 1:2).
Notice how this makes for an infinitely higher standard. The Lord said to His followers, "A new commandment I give to you, that you love one another; as I have loved you, that you also love one another" (Jn. 13:34). It wasn't a "new" commandment that they love one another. They had that in the Jewish Law (Lev. 19:18, 34). What was new was that "as I have loved you." Christ-like love is the goal.
The standard of the New Testament is that, once we've put our faith in Christ for salvation, we continue to "grow in the grace and knowledge of our Lord and Saviour Jesus Christ" (II Pet. 3:18). "Till we all come to the unity of the faith and of the knowledge of the Son of God, to a perfect man, to the measure of the stature of the fullness of Christ" (Eph. 4:13).
"We all, with unveiled face, beholding as in a mirror the glory of the Lord, are being transformed into the same image from glory to glory, just as by the Spirit of the Lord" (II Cor. 3:18). This is where the fruit of the Spirit comes in (Gal. 5:22-23)--it's a kind of summary of Christ-like character. By the ongoing work of the indwelling Holy Spirit, Christians are being "conformed to the image of His Son" (Rom. 8:29).
It is, of course, a standard that is impossible to reach in this life. None of us is able to claim perfection (I Jn. 1:8, 10). But it's what we are to aim for. And there is a means of cleansing when we fall short (I Jn. 1:9; 2:1-2). Praise the Lord we have the prospect of being made "like Him" at the resurrection (Phil. 3:20-21; I Jn. 3:2), "and everyone who has this hope in Him purifies himself [day by day], just as He is pure" (I Jn. 3:3).