Fellow Christians, what can you add to a person's claims about Christian salvation, that you only need to believe in Jesus. Is this true?

In one sense, I believe that is true, if you narrowly define "being saved" as getting admitted to heaven after you die. 

But in another sense, "being saved" is something that lasts throughout your life, and is about being changed to become more like Christ as you are guided and enabled to leave your old habits of sin behind and become a new kind of person to fulfill your purpose in life- something constructive and not destructive. This process requires you to make every effort to focus on and obey God's teaching in your life.

Just as with habits that make you physically healthy, habits that make you spiritually healthy should be pursued consistently, because if you go too long without progressing, you are sure to regress.

If you don't believe God, then what good are you to Him? Hence, salvation through faith, only. It is the starting point for believing God and trusting God. 

What you probably should have mentioned is that God, as a result of one repenting and believing the gospel, gives that person His Holy Spirit; a new heart. God changes the person into a son/daughter of God, now capable of producing good fruits "wrought in God." 

You are confusing yourself. It's not complicated. Read the Nicene Creed. That is the simplest written form of the Christian faith.

Sola Fide is a fallacious doctrine. 

A person must believe the truth, to gain salvation - 1 Timothy 2:4 – whose (God’s) will is that all sorts of people should be saved and come to an accurate knowledge of truth. - - - - As that Scripture makes clear, what a person believes must be the truth, in order to be saved. One must come to KNOW both, God and Christ to gain everlasting life - John 17:3 - This means everlasting life, their coming to know you, the only true God, and the one whom you sent, Jesus Christ. - - - - Just as Jesus said, a person must come to know him and his Father. And Jesus made clear exactly where we find the truth, that is accurate knowledge about him and his Father - John 17:17 - Sanctify them by means of the truth; your word is truth. - - - - So what does God's word of truth say about Jesus and his Father? Jesus NEVER claimed to be God. He clearly stated that he IS God's Son - John 10:36 - do you say to me whom the Father sanctified and sent into the world, ‘You blaspheme,’ because I said, ‘I am God’s Son’? - - - - God's word of truth even shows that it would have been tantamount to a seizure, for Jesus to even think that he was equal to God - Philippians 2:6 - who, although he was existing in God’s form, gave no consideration to a seizure, namely, that he should be equal to God. - - - - So, in order to gain salvation, one must understand the truth that Jesus is NOT God! - - - - To further emphasize that Jesus is not God, is to understand that God NEVER died. If he had, how could he be resurrected? Since God's word of truth makes clear that the dead have no knowledge at all. They know nothing at all - Ecclesiastes 9:5 & 10 - 5 For the living know that they will die, but the dead know nothing at all, nor do they have any more reward, because all memory of them is forgotten. 10 Whatever your hand finds to do, do with all your might, for there is no work nor planning nor knowledge nor wisdom in the Grave, where you are going. - - - - If God died, it would be contrary to His word of truth for Him to have knowledge in death. And God's word is not contradictory. Because the truth cannot be contradictory. For example, either God is a trinity, or He is not. Both cannot be true. And either Jesus is God, or he is not. Both cannot be true. Thus, if God's word is the truth as Jesus said it is, it cannot be contradictory. - - - - Since God wants everyone to have an accurate knowledge of the truth, He tells us in His word how to make sure we obtain accurate knowledge - Acts 17:11 . . . carefully examining the Scriptures daily to see whether these things were so. - - - - Since the truth cannot be contradictory, we can examine the Scriptures carefully. To make sure we are getting the truth. We can also approach God in prayer and ask for His help in making sure we get the truth from His word - Psalm 65:2 - O Hearer of prayer, to you people of all sorts will come. - - - - With that in mind, I urge everyone to approach God in prayer and ask for His help in discerning what is true and what is not. Free Bible lessons are offered online at the following web site. But ALWAYS examine the Scriptures carefully. To make sure you are indeed getting the truth that leads to salvation. The site is:

www.jw.org

"Believe in" Jesus, meaning accepting His teaching and living by it. Not just believing He existed.

Anonymous, talking about John 3:16 - you also blocked me. Are you the same person as the above person? It is not good to lie and pretend to be different people, if you are the same person. Christians should witness openly who they are.

Second, there is also the verse John 3:36, which is often translated as:

"He who believes in the Son has eternal life; he who does not obey the Son shall not see life, but the wrath of God rests upon him"

Some translations say "he who does not believe in the Son" like KJV, but in the original greek these are different words: pisteuōn - believing and apeithōn - not obeying.

https://biblehub.com/interlinear/john/3-36.htm

"Keeping commandments" isn't about heaven and hell.  It is about other issues, like honoring the Lord and helping others.  Matthew 7:21, the will of the Father is believing in the Lord Jesus Christ.  Doing good works are good for other reasons.  But don't add any works to getting into heaven.  Romans 4:5.  You are on the path to hell with your "works", so beware.

Remember that all Christian denominations teach different truths. That person is in delusion if he believes that he knows the truth.

Technically, that’s true.  Belief and faith in Jesus is all that is required.  Unfortunately, that equates to many believers as just mentally acknowledging that Jesus existed, and that’s not what it means.

 “Believing” in him means following  him and imitating him, making him your master.