Believing on Jesus Christ means believing in his requirements that he has given to us.
Believing on Jesus Christ means we are trusting in Him alone for salvation/trusting in His death, burial and resurrection as the ALL-sufficient means of our salvation. (Acts 10:43; 16:31; Romans 1:16; 1 Corinthians 15:1-4) John 6:28 - Then they said to Him, “What shall we do, that we may work the works of God?” 29 Jesus answered and said to them, “This is the work of God, that you
believe in Him whom He sent.”
Many people came to Jesus asking to follow him, some of them having kept the commandments, tithing, etc etc etc. Jesus turned them away because they refused to do what he told them to do. It is even said that one went away sad, because he probably was very much interested in the salvation that Jesus offered but could not do a very difficult thing that Jesus required of him.
In John chapter 6, we see that many of Jesus' so called disciples complained and were offended (verses 60-61) about what Jesus said in verses 51-59. These are the very so called "disciples" who Jesus says
“do not believe.” (John 6:64) They also
walked with Him no more. So apparently, these alleged disciples of Jesus set out to be learners and followers of Him (based on their own expectations) of Jesus, then as soon as Jesus said something that was hard for them to understand and did not line up with their expectations, they left Him.
In regards to the rich young man in Matthew 19:16-22, Jesus showed him how short he falls of keeping the first commandment (Exodus 20:3) which is the first of the two great commandments (Deuteronomy 6:5; Matthew 22:37) by trusting in his riches over Christ could not part from his great wealth, not even in exchange for eternal life. The rich young ruler confidently and (self righteously) declared that he has kept the commandments from his youth up and qualified for heaven under those terms. Yet Jesus knew the man's wealth had become his idolatrous god, which kept him from believing in Jesus unto salvation.
Believing in Jesus means that you believe in all the words that he says concerning salvation. Jesus himself did much work as he said he came to earth to finish his father's work. God worked. Jesus worked (He was obedient unto death). Paul worked. And it seems strange that we as his children are not required to work. In fact we are promised rest from our work after we have finished his will.
John 3:16 - 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 3:18 - He who
believes in Him is not condemned; but he who
does not believe is condemned already, because he has not believed in the name of the only begotten Son of God.
John 6:40 - For my Father’s will is that everyone who looks to the Son and
believes in him shall have eternal life, and I will raise them up at the last day.
John 6:47 - Most assuredly, I say to you, he who
believes in Me has everlasting life.
John 11:25 - Jesus said to her, “I am the resurrection and the life; he who
believes in Me will live even if he dies, 26 and everyone who lives and
believes in Me will never die. Do you believe this? I certainly do.
Knowing his will is the most important thing in all of Christianity. If you know his will, it means that you have found the truth and the truth will set you free.
What is His will for us in regards to receiving eternal life? John 6:40 - John 6:40 - For
my Father’s will is that everyone who looks to the Son and
believes in him shall have eternal life, and I will raise them up at the last day.
John 4:34 Jesus saith unto them, My meat is to do the will of him that sent me, and to finish his work.
That was the will of the Father for Jesus to do.
Heb_4:10 For he that is entered into his rest, he also hath ceased from his own works, as God did from his.
Heb_4:11 Let us labour therefore to enter into that rest, lest any man fall after the same example of unbelief.
The writer of Hebrews is talking about our "sabbatismos" rest (Hebrews 4:9) that we have in Christ. No matter how rigorously people labor, they could never earn their way to heaven by their works/performance. Labor here involves continuing in belief rather than fall in unbelief.
Rom 12:2 And be not conformed to this world: but be ye transformed by the renewing of your mind, that ye may prove what is that good, and acceptable, and perfect, will of God.
This is the will of God for believers after they have been saved. We also see the will of God for believers (those already saved) in 1 Thessalonians 5:14-18: Now we
exhort you, brethren, warn those who are unruly, comfort the fainthearted, uphold the weak, be patient with all. See that no one renders evil for evil to anyone, but always pursue what is good both for yourselves and for all. Rejoice always, pray without ceasing, in everything give thanks;
for this is the will of God in Christ Jesus for you.
WE MUST NOT CONFUSE GOD'S WILL FOR US TO BECOME SAVED WITH GOD'S WILL FOR US AFTER WE HAVE BEEN SAVED.