John 3:16 is still the best answer to the question of what must I do to be saved. It’s more than “merely” believing in God, it’s understanding that God gave His Son, Jesus, to die the death we deserved (Romans 5:6-11). He took our place. Believe that, accept that and salvation is yours. That’s the promise of John 3:16.
Accepting this gift from God does bring a response. In the same chapter of John, when Jesus is talking to Nicodemus, He tells him he must be born again (John 3:3-8). Jesus is speaking of a spiritual rebirth when we become children of God (John 1:12). God is our Father. We are family. God loves us--He’s shown that. Having accepted His love, our response is to love Him in return. This leads to relationship building as we try to understand Him better through talking with Him, studying His ways, and being part of His family (have you ever noticed how you find glimpses of the parents in children--in the way they look, act, or handle situations?).
“Merely believe” is not adequate to describe the life-changing event of understanding what God has done for us and accepting it, but you are right about developing a close relationship with Him. It’s the relationship we build with Him that keeps us in His family.
Has our salvation already been determined?
God allows humans freedom of choice. That began in the Garden of Eden--Adam and Eve could choose to follow God’s ways or not. Love does not lead by force.
It’s God’s love that takes centre stage in John 3:16 where it says God loved so much that He gave Jesus “so that everyone who believes in him would not perish but have eternal life” (NLT). We choose whether to believe or not. With the poor choice in Genesis, God pleads for the best choice in Revelation with Jesus pictured standing at our heart’s door knocking, waiting to be invited in (Revelation 3:20). It’s our choice as to how we respond. Salvation is only found in opening the door.
Even after we choose to follow God and accept Jesus we still have the freedom to reject Him. You find that illustrated in the tragic story of Demas, who is listed as one of Paul’s helpers (Colossians 4:14). Paul reports at a later time that Demas has “deserted me because he loves the things of this life” (2 Timothy 4:10, NLT). Our salvation is determined by the choices we make.
No. Our good works will never get us into heaven because they are not good enough. The standard of works would have to be absolute perfection and we always fall short (Romans 3:23). Good works don’t even get us on the first rung of the ladder to heaven. It isn’t the “relatively good life” that gets us to heaven, but our relationship to the Savior.
Listen: “We are made right with God when we believe that Jesus shed his blood, sacrificing his life for us. . . . Can we boast, then, that we have done anything to be accepted by God? No, because our acquittal [from sin] is not based on our good deeds, it is based on faith” (Romans 3:25, 27, NLT). Good works come out of this faith relationship with God, not to gain a place in heaven, but because we are already a part of God’s kingdom.
God is concerned for our quality of life. Jesus said that He had come "that they may have life, and have it to the full.” (John 10:10 NIV) Or as it says in the King James Version, to have life “more abundantly.” The illustrations you give--jewelry and vegetarianism--are matters that fall into this category of living the best life possible. They are based on principles that come from the Bible--God's guidebook for how you can live the happiest, healthiest, most productive life possible.
Now in some parts of the world, limited food choice may mean that it's not possible to get proper nutrition through a vegetarian diet. But where there is abundant food choice, a vegetarian diet is clearly the optimum. Or take the principles of simplicity and modesty. In some parts of the world you will find that some Adventists wear engagement rings, and with the church’s blessing. Where this happens, the church has recognized that an engagement ring plays an important part in demonstrating the promise to marry. In other places, where it does not have the same significance, it is discouraged by the church.
No one will go to heaven because they don’t wear jewelry or don't eat meat. We will be there because we have placed our faith in Jesus (Romans 3:22). But the lifestyle questions are important because how you live, including what you eat and how you dress, is a part of your response to God’s love gift of life eternal.
How can I be sure of my salvation?
You can be sure of your salvation by being sure of your Savior. Focus on what God has done, not on what you have done. God emptied heaven for you when He gave Jesus to die. Jesus’ resurrection demonstrated that death has been conquered. Because of what God has already done through Jesus we can trust His promise to return. It’s important to keep our focus on God because if we look to ourselves and our personal weaknesses or our feelings, we will doubt.
Be assured that our salvation is in Jesus, through faith in Him and what He has done (John 3:16; read Romans 3). Here are some thoughts that may help you: Jesus came to the world not to condemn it, but to save it (John 3:17). There is nothing that can separate us from the love of God (Romans 8:31-39). It’s as if we His followers were raised from the dead with Christ and are even now seated with Him in heaven (Ephesians 2:6). “We are God’s masterpiece. He has created us anew in Christ Jesus” (Ephesians 2:10, NLT).
One letter of the New Testament was written “to you who believe in the Son of God, so that you may know you have eternal life” (1 John 5:13, NLT). First John begins by introducing Jesus and then assuring us that our confessed sins will be forgiven. The rest of the letter emphasizes in a variety of ways that we should love God and love each other, along with a call to live as children of God. Salvation’s emphasis must always be on Christ. There’s no certainty anywhere else.
Is circumcision a requirement for salvation for Christian males?
No. The apostle Paul used strong language against those who took that position: “Watch out for those dogs, those wicked men and their evil deeds, those mutilators who say you must be circumcised to be saved” (Philippians 3:2, NLT). In answer to this question, Philippians 3:1-11 is worth reading. Paul tells his own story and the fact that he was circumcised like a “real Jew” and followed the law with strictest obedience. However, all this was worthless because of what Christ has done. “I trust Christ to save me,” he says. (You will find a similar message in Galatians 5:1-12.)