Do we only need to believe on Jesus in order to be saved?
I believe that this question is grossly misrepresented and often times misused. The passage I'm referring to is John 3:16 For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life. and it's counter part John 6:47 Verily, verily, I say unto you, He that believeth on me hath everlasting life.
If you look at these scriptures as a stand alone with no supporting scripture it can be very misleading. The Bible is written that one verse leads into another. Often the verse can be next to each other or many books apart. To find the full meaning of any scripture we need to look to the Holy Spirit to show us the whole truth, not just bits and pieces. The Bible tell us that we are to search the scriptures as in Luke 11:9 And I say unto you, Ask, and it shall be given you; seek, and ye shall find; knock, and it shall be opened unto you.
According to John 3:16 there is nothing else that you need to do but believe on Jesus. However this a very important and essential part of our walk toward salvation, but it is not the whole picture. One thought that comes to mind is that by this passage alone, this would mean that Satan would be saved for all of eternity. Satan knows and believes that Jesus is the only begotten son of God and is the second person in the God head or the Trinity (God the Son). But this certainly does not mean that Satan is going to inherit eternal life in heaven with the saints.
We know this by reading the verse in Mark 3:11 And unclean spirits, when they saw him, fell down before him, and cried, saying, Thou art the Son of God. and again in Mark 5:7 And cried with a loud voice, and said, What have I to do with thee, Jesus, thou Son of the most high God? I adjure thee by God, that thou torment me not.
So we can clearly see that Satan knows who Jesus is and the power he possesses. We all know that Satan will not be spending any time in heaven after he is cast out in Revelation 12:7 And there was war in heaven: Michael and his angels fought against the dragon; and the dragon fought and his angels, (8) And prevailed not; neither was their place found any more in heaven. (9) And the great dragon was cast out, that old serpent, called the Devil, and Satan, which deceiveth the whole world: he was cast out into the earth, and his angels were cast out with him.
The whole picture:
John 3:16 For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.
Luke 18:18 And a certain ruler asked him, saying, Good Master, what shall I do to inherit eternal life? (20) Thou knowest the commandments, Do not commit adultery, Do not kill, Do not steal, Do not bear false witness, Honour thy father and thy mother. (21) And he said, All these have I kept from my youth up. (22) Now when Jesus heard these things, he said unto him, Yet lackest thou one thing: sell all that thou hast, and distribute unto the poor, and thou shalt have treasure in heaven: and come, follow me. (23) And when he heard this, he was very sorrowful: for he was very rich. (24) And when Jesus saw that he was very sorrowful, he said, How hardly shall they that have riches enter into the kingdom of God! (25) For it is easier for a camel to go through a needle's eye, than for a rich man to enter into the kingdom of God. Take notice that the in the scriptures above, it does not mention that you have to believe in order to be saved, but that you need to follow and and hold to the commands that God has laid down for us to put into practices. Both in John 3:16 and Luke 18:18-25 must be met in order to be saved.
Revelation 22:14 Blessed are they that do his commandments, that they may have right to the tree of life, and may enter in through the gates into the city. Here we are instructed that in order to have rights to the tree of life (to be saved) we must do his (Jesus') commandments. The commandments are listed in Exodus chapter 20 Exodus 20:1 And God spake all these words, saying,
Exodus 20:2 I am the LORD thy God, which have brought thee out of the land of Egypt, out of the house of bondage.
Exodus 20:3 Thou shalt have no other gods before me.
Exodus 20:4 Thou shalt not make unto thee any graven image, or any likeness of any thing that is in heaven above, or that is in the earth beneath, or that is in the water under the earth:
Exodus 20:5 Thou shalt not bow down thyself to them, nor serve them: for I the LORD thy God am a jealous God, visiting the iniquity of the fathers upon the children unto the third and fourth generation of them that hate me;
Exodus 20:6 And shewing mercy unto thousands of them that love me, and keep my commandments.
Exodus 20:7 Thou shalt not take the name of the LORD thy God in vain; for the LORD will not hold him guiltless that taketh his name in vain.
Exodus 20:8 Remember the sabbath day, to keep it holy.
Exodus 20:9 Six days shalt thou labour, and do all thy work:
Exodus 20:10 But the seventh day is the sabbath of the LORD thy God: in it thou shalt not do any work, thou, nor thy son, nor thy daughter, thy manservant, nor thy maidservant, nor thy cattle, nor thy stranger that is within thy gates:
Exodus 20:11 For in six days the LORD made heaven and earth, the sea, and all that in them is, and rested the seventh day: wherefore the LORD blessed the sabbath day, and hallowed it.
Exodus 20:12 Honour thy father and thy mother: that thy days may be long upon the land which the LORD thy God giveth thee.
Exodus 20:13 Thou shalt not kill.
Exodus 20:14 Thou shalt not commit adultery.
Exodus 20:15 Thou shalt not steal.
Exodus 20:16 Thou shalt not bear false witness against thy neighbour.
Exodus 20:17 Thou shalt not covet thy neighbour's house, thou shalt not covet thy neighbour's wife, nor his manservant, nor his maidservant, nor his ox, nor his ass, nor any thing that is thy neighbour's.
Some would argue that the commandments were done away with in the New Testament. This is a false statement, for we just read in Luke 18:20 Thou knowest the commandments, Do not commit adultery, Do not kill, Do not steal, Do not bear false witness, Honour thy father and thy mother. Here Jesus clearly states that these commandments are still in affect today and need to be kept.
Act 15:11 But we believe that through the grace of the Lord Jesus Christ we shall be saved, even as they. That we believe through grace.
Act 16:31 And they said, Believe on the Lord Jesus Christ, and thou shalt be saved, and thy house. Again this states that we need to believe on Jesus Christ in order to be saved. Jesus is the only way we can be saved.
Romans 10:9 That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved. We also need to confess verbally our belief to our fellow man. We are not to hide out light under a bushel but let our light shine for all to see (Luke 11:33).
** Note all references are taken from the King James Version.