I. People are commanded by God/Jesus or an apostle to believe in Jesus Christ in order to have eternal life or be saved.
A. In Mark 1:14-15 Jesus commanded people to repent and believe in (put their trust in) the gospel. They were to change their thinking about their present object of trust (Gk. “metanoeo” – “repent”), such as being a Jew, a son of Abraham (Matt. 3:9), and commit themselves wholeheartedly to a new object of faith (Gk. “pisteute en” – “believe in”), that object, here, being the gospel/good news, which is Jesus Christ as the Messiah, the Son of God (Mk. 1:1) – J. Walvoord and R. Zuck, The Bible Knowledge Commentary, New Testament, p. 107.
B. In John 6:27-29 Jesus tells the Jews that in order to have eternal life they must work/do the works/requirements of God, and the work/requirement of God is that they believe in Him/Jesus whom God the Father sent. And to believe in Jesus Christ is to believe in Him as the bread of life (Jn. 6:35), the eternal life giver (Jn. 6:33, 47), the Christ/Messiah, Son of the living God (Matt. 16:16). The “work” of God is the action required of God, the acceptable obedience, and that is to believe in Jesus Christ (Jamieson, Fausset, and Brown, Commentary on the Whole Bible, p. 1039).
C. In Acts 16:30-31 Paul and Silas command the jailer to believe in the Lord Jesus Christ to be saved. “Pisteuson” is in the first aorist active imperative, second person singular – “you believe” – which is a command (A.T. Robertson, Word Pictures in the New Testament, vol. 3, p. 262).
D. In 1 John 3:23 the apostle John states that it is God’s commandment that we believe in the name of His Son Jesus Christ. So, to obey this command is to believe in Jesus Christ (who He is – the Savior, which is what “Jesus” means and Christ/Messiah, which is God’s Son and Redeemer as seen in Isa. 53:5 and Jn. 1:29 – who died as a sacrificial Lamb for our sins).
So, we see that to obey God/Jesus in the area of what it takes to be saved or have eternal life is to believe in Jesus Christ as Savior.
II. To obey is to believe.
A. In Rom. 10:13-16 Paul states that the Jews did not all heed (“hypekousan” means “to hear with a positive response, and so to obey, to submit to” – Walvoord and Zuck, The Bible Knowledge Commentary, New Testament, p. 484) the glad tidings/gospel; for Isaiah says, “Lord, who has believed our report?” So, to heed/obey the glad tidings/report was or is to believe the report/tidings.
B. In Rom. 1:5; 16:25-26 and Acts 6:7 Paul uses the phrase “obedience of faith” or “obedience to the faith”. Paul was an apostle to bring about the obedience of faith among all the Gentiles, for His/Christ’s name sake. In other words, people were yielding to the belief of God’s saving message (Jamieson, Fausset, and Brown, Commentary on the Whole Bible, p. 1140); faith is regarded as an act of obedience or commitment to the gospel of Christ (John Murray, The Epistle to the Romans, p. 13); the act of faith is the obedience of the understanding to God revealing, and the product of that is the obedience of the will to God commanding (Matthew Henry’s Commentary, vol. 3, p. 931). In Rom. 16:25-26 the preaching of the gospel of Jesus Christ had been made known to all the nations, leading to obedience of faith. In other words, “believing acceptance” (Jamieson, Fausset, and Brown, p. 1134); faith in the gospel (J. Murray, p. 243); obedience to the gospel (Matthew Henry, p. 1013).
III. Disbelieving is disobeying, and disobeying is disbelieving.
A. In 1 Pet. 2:7-8 Peter states that those who disbelieve Christ, the choice stone, a precious corner stone (1 Pet. 2:6) are those who rejected Christ, the stone, and are those who stumbled over Christ, a stone of stumbling because they are disobedient to the word. So, to disbelieve in Christ is to be disobedient to the word of God, which is the good news about Christ for salvation (1 Pet. 1:3, 7-9, 23).
B. In Rom. 15:31 Paul asks the Roman Christians to pray for him to be delivered from those who are disobedient in Judea. And the disobedient are the disbelievers, as seen in Acts 22:17-18; 25:18-19; 26:17-23 (“they will not accept your testimony about Me” – Jesus – Acts 22:18).
C. In 1 Pet. 4:17-18 Peter asks, “…what will be the outcome for those who do not obey the gospel of God?” And how does a person not obey the gospel of God (i.e., the good news that Christ died for our sins, was buried, and was raised on the third day – 1 Cor. 15:1, 3-4)? By not believing it, as Rom. 10:16 already showed. This is also seen by the contrast of those who don’t obey the gospel with those who are of the household of God (righteous and saved – 1 Pet. 4:17-18). And those who are of the household of God, righteous, and saved are those who have obeyed the gospel by believing it (Rom. 1:16-17; 16:25-26; Col. 1:4-5; Eph. 1:13-14; Jn. 1:12).
In 2 Thes. 1:8-9 Jesus is said to deal out retribution to those who do not obey the gospel of our Lord Jesus, and that they will pay the penalty of eternal destruction away from the presence of the Lord. Not believing in the good news about Christ as Savior is what causes this judgment (Jn. 3:18), whereas belief in Jesus Christ as Savior spares believers from this judgment of retribution and instead gains believers eternal life with Christ (Jn. 3:16, 18; 2 Thes. 1:10).
D. In Jn. 3:36 it states that “he who believes in the Son has eternal life; but he who does not obey the Son shall not see life, but the wrath of God abides on him” (New American Standard Bible). The Greek word “apeithon” means “obeys not” (A.T. Robertson, Word Pictures in the New Testament, vol. 5, p. 57). W.E. Vine, M. Unger, and W. White Jr. in An Expository Dictionary of Biblical Words, New Testament, pp. 796, 797 defines “apeitho” as “disobey” or “not persuaded”. The King James Bible translates it as “disbelieves”, while the New International Version translates it as “rejects”. So, to not obey the Son is to reject, disbelieve, not be persuaded about the Son. This also makes sense because “apeithon” stands in contrast to “believe” in this verse and is identical to the parallel thought in Jn. 3:18 (“believes” and “not believed”).
IV. Obeying Christ/God is believing Christ/God.
A. 1 Pet. 1:1-9 Peter states that certain people are chosen by God and set apart (“sanctified”) by the Holy Spirit so that they may obey Jesus Christ and be sprinkled by His blood. A parallel passage is found In 2 Thes. 2:13, where it states that God had chosen them for salvation through setting them apart (“sanctification”) by the Holy Spirit and faith in the truth. The “truth” is the gospel of salvation found in Jesus Christ Himself (Eph. 1:13; Jn. 14:6; Col. 1:5; 2 Thes. 2:10, 12-13). To obey Christ is to believe in Christ, the truth. And what allows a person to be sprinkled by Christ’s blood (cleansed, forgiven of our sins)? Faith in Christ (Acts 15:9; Rev. 1:5; Rom. 3:24-25; Eph. 1:7).
B. In Heb. 5:9 it states that Jesus became to all those who obey Him the source of eternal salvation. As has already been shown, to obey Jesus as it relates to salvation has the meaning of believing in Jesus as Savior and Son of God. However, if obedience were to be taken in its normal meaning of “to follow the command of” or “to comply with”, then it would have reference to the command in Mk. 1:15 or John 6:29 of believing in Christ whom God the Father sent to earth as Savior (Homer Kent Jr., The Epistle to the Hebrews, p. 101).
C. In Acts 5:32 it states that God has given the Holy Spirit to those who obey Him/God. When did people in the New Testament Church Age receive the Holy Spirit? According to Acts 10:42-45; 11:14-17; 15:7-8 these people received the Holy Spirit upon/after believing in the Lord Jesus Christ. The Greek word “pisteusasin” is in the first aorist (meaning “upon completion of the act”) active participle in the dative case (meaning “after believing”). Eph. 1:13-14 teaches the same thing, that it was upon/after believing the gospel of salvation of Jesus Christ. Therefore, to obey God means to obey His command, in 1 Jn. 3:23, to believe in Jesus Christ.
In conclusion, to obey is to believe when it refers to the issue of salvation (eternal life, the gospel, the Holy Spirit, Jesus Christ, or God the Father).