Sin is the breaking of God’s moral law (which reaches back to Creation and is embodied in the spirit and letter of the Ten Commandments).
Everyone has broken God’s law. (Rom 3:23)
The penalty ("wages") of sin is death. (Rom 6:23)
This is not the death that happens when our life ends.
This is the "second death" (Rev 20:6) which will happen to the lost when they cease to exist in any form, forever.
Salvation is God’s act of saving us from the penalty of sin. 
God makes it perfectly clear that there is only one way to be saved. 
There is only one way to Heaven.
Jesus is the Way. (John 14:6)
We are saved solely by God’s grace, through faith (belief) in Jesus and His atoning sacrifice for our sins. 
We are saved the moment we are justified (made righteous in God’s eyes and fitted for Heaven). 
When we confess and repent of our sins, and in sincerity ask God for forgiveness in Jesus’ name, God attributes to us Christ’s righteousness.
(To repent means to be sorry for and to turn away from).
There is absolutely nothing that we can do of ourselves to earn our salvation.
It is not a reward, it is a gift.
You don’t earn a gift. If you did earn a gift in any way, it wouldn’t be a gift.

For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord.
— Romans 6:23


49. At the core of all false religion is the idea of salvation by works in one form or another. “The principle that man can save himself by his own works lay at the foundation of every heathen religion. . . Wherever it is held, men have no barrier against sin.”

50. No person will be justified before God by the works of the law, because those who are justified before God are made thus by His faithfulness, not by their own (Romans 3:20-22).

51. The objective reality of salvation is an accomplished fact in Christ. Our subjective experience of that salvation contributes nothing to our salvation, adds no increased merit or better standing before God (Romans 3:24).

52. There is nothing you can do to earn God’s love, because He already loves you and there’s nothing you can do to make Him stop (Romans 8:35-39).

53. ”Reliance upon human merit intercepts the view of Christ’s infinite love.”

54. Legalism is a subtle form of self-centredness. It allows me to maintain my obsession with myself while pretending it’s all about God (Philippians 3:2-11).

55. Attitudes of moral superiority often hide actions of moral degradation, and condemnation of others is often a cloak for secret sin (Romans 2:1-3).

56. “There is not a point that needs to be dwelt upon more earnestly, repeated more frequently, or established more firmly in the minds of all than the impossibility of fallen man meriting anything by his own best good works. Salvation is through faith in Jesus Christ alone.”

You might ask: what about all those people who lived before Jesus and all those who have never heard His name?
Since Creation, salvation has always been a matter of faith; faith that confession of and repentance for sins will result in God’s forgiveness.
This forgiveness has been available through the confessor’s sins being borne by a Messiah (promised to Adam and Eve), a literal sacrificial lamb and finally the Lamb of God (Jesus).
God gives everyone a chance to respond to the Holy Spirit’s call on their heart, on their conscience, to confess, repent and turn away from sin.
We all know right from wrong, and salvation is available to us all until we die, unless we continue in committing the "unpardonable sin".
Those who respond to the call of God’s Spirit, and live up to the "light" they have received from God, will be saved.
Those who reject God’s call will be lost.
We don’t have all the answers as to how God will judge everyone who has ever existed.
We must simply trust God as the perfect judge.

Here is a video clip that touches on this subject.

Here's another perspective:
"Even among the heathen are those who have cherished the spirit of kindness; ..."

Recommended audio below.

A popular misconception is that once we are "saved", that’s it; we are guaranteed a place in Heaven.
This "once saved, always saved" doctrine is not Biblical and is extremely dangerous; it is (eternal-) life-threatening.
If we willingly choose to continue to sin after once being justified, then the sacrifice of Jesus is to no effect and we will again be lost. Rom 6:15-16; Heb 10:26-27

"Why should I bother with religion? I’m a good person.
I haven’t robbed a bank or killed anyone.
I’m honest on my tax return and I don’t cheat on my wife.
I donate to charity, in fact I sponsor an orphan in India.
If there’s a heaven then I’ll be there, because I deserve to be."
Something along these lines could be in the minds of many people you and I know.
Sadly, but of necessity, Heaven is not automatic. 
Jesus is the only way to Heaven. (Acts 4:12)
If we reject God’s call to make Jesus the Lord of our life, we will be lost.
That’s the plain fact.
There will be many tears for God to "wipe away". (Rev 21:4)

God will rid the universe of sin, and sinners, at some time in the future, when Jesus returns.
Sin results in suffering and God doesn’t want anyone to suffer, because He loves us all so much.
He has given us a way out through His infinite Sacrifice on the Cross.
He offers us an eternity of perfect peace, joy and wonders beyond imagination..all for free.
Why would anyone reject God’s gift?

God’s justice is tempered with mercy. His plan of salvation shows that mercy which, like His justice, results from His love for us.
God, in the person of the Word (Jesus), the Creator of the universe, became one of His own creations.
He identified with our humanity by becoming human. Incredible.
He took on all our sins and paid the price for them.
He faced eternal death, and chose to risk ceasing to exist so that we might live.
On the Cross, Jesus could not see past the grave.
He did not have assurance of His resurrection at that point.
He was totally cut off from the Father and from all of Heaven.
Despite the complete darkness within Him, He went through this agony of separation and torment for us.
He chose our eternal life ahead of His own.

The Bible tells us that Jesus will retain for eternity our human nature, and His physical human form (albeit "glorified"), while relinquishing His pre-incarnation divine attributes such as omnipresence and omnipotence.
The verses are there: Acts 1:9-11; Phil 2:5-11; Phil 3:20-21 and perhaps others.
Jesus will return as He left, as Jesus the "Son of Man". There won't be a second incarnation. He won't be doing a quick-change act.
Jesus was perfect, hence His sacrifice was perfect and sufficient.
His sacrifice, however, is not limited to 33 years on this planet and risking His eternity on the Cross.
That, in itself, would be much, much more than we deserve.
Jesus’ sacrifice is eternal, infinite.
He gave up His divine power and presence forever! ...for us!
He knew exactly what He was to forfeit (at the very least!), however He went ahead with it. He agreed to the plan.
That’s how closely He relates to us.
That’s how much He cares about us...every single person.
Yes, that’s how much He loves us, but that’s also how much He likes us!

He wants to be our friend, and moreover our brother.
It's as simple and as beautiful as that.

Think about it.
What sort of God do we have?
The best God imaginable.
His plan of salvation fits perfectly.