Salvation is not possible without first believing in Jesus' sacrifice as payment for all of the sins of humanity. However, according to many scriptures it is apparent that each individual must believe and obey the rest of the message.
If you think that individuals must "obey the rest of the message" to be saved, then you do not understand the gospel at all.
But, to clarify, what, exactly is included in "the rest of the message", just so I can better understand your position.
This NT message includes the command to repent, and be baptized in the name of the Lord Jesus Christ for the remission of one's personal sin. The scripture states that EVERYONE is to be obedient to the command. (Acts 2:38) In addition, God will provide the gift of the Holy Ghost. (Acts 2:33) And this can take place before or afterward as witnessed in scripture.
Define "repent".
Acts 2:38 was a specific message to the very Jews who were involved directly in the crucifixion. What Peter said to them doesn't apply to anyone else.
Here are some verses to examine.
Salvation:
Luke 8:12 "Those beside the road are those who have heard; then the devil comes and takes away the word from their heart, so that they will not believe and be saved.
Acts 4:12 "And there is salvation in no one else; for there is no other name under heaven that has been given among men by which we must be saved."
Acts 11:14 and he will speak words to you by which you will be saved, you and all your household.'
Acts 16:31 They said, “Believe in the Lord Jesus, and you will be saved, you and your household."
Rom 10:9, 10 9 that if you confess with your mouth Jesus as Lord, and believe in your heart that God raised Him from the dead, you will be saved; 10 for with the heart a person believes, resulting in righteousness, and with the mouth he confesses, resulting in salvation.
Rom 1:16 For I am not ashamed of the gospel, for it is the power of God for salvation to everyone who believes, to the Jew first and also to the Greek.
1 Cor 1:21 - For since in the wisdom of God the world through its wisdom did not know him, God was pleased through the foolishness of what was preached to save those who believe.
Eph 2:8 For by grace you have been saved through faith; and that not of yourselves, it is the gift of God;
2 Tim 3:15 and that from childhood you have known the sacred writings which are able to give you the wisdom that leads to salvation through faith which is in Christ Jesus.
1 Peter 1: 5 who are protected by the power of God through faith for a salvation ready to be revealed in the last time.
1 Peter 1:9 obtaining as the outcome of your faith the salvation of your souls.
2 Thess 2:13 But we should always give thanks to God for you, brethren beloved by the Lord, because God has chosen you from the beginning for salvation through sanctification by the Spirit and faith in the truth.
Eternal Life:
John 3:15-16 15 so that whoever believes will in Him have eternal life. 16 "For God so loved the world, that He gave His only begotten Son, that whoever believes in Him shall not perish, but have eternal life.
John 3:36 "He who believes in the Son has eternal life; but he who does not obey the Son will not see life, but the wrath of God abides on him."
John 5:24 "Truly, truly, I say to you, he who hears My word, and believes Him who sent Me, has eternal life, and does not come into judgment, but has passed out of death into life.
John 6:40 "For this is the will of My Father, that everyone who beholds the Son and believes in Him will have eternal life, and I Myself will raise him up on the last day."
John 6:47 "Truly, truly, I say to you, he who believes has eternal life.
Rom 6:23 For the wages of sin is death, but the free gift of God is eternal life in Christ Jesus our Lord
1 Tim 1:16 Yet for this reason I found mercy, so that in me as the foremost, Jesus Christ might demonstrate His perfect patience as an example for those who would believe in Him for eternal life.
Gal 3:22 But the Scripture has shut up everyone under sin, so that the promise by faith in Jesus Christ might be given to those who believe.
1 John 5:13 These things I have written to you who believe in the name of the Son of God, so that you may know that you have eternal life.
No mention of obedience. Only believing (faith).
When man believes what Jesus did on the cross, God saves.