God has made a very clear promise to all those who believe in His Son, that He will forgive them, give them eternal life, and keep them forever in His love.
Come now and let us reason together, says the Lord, though your 
sins are as scarlet, they will be as white as snow; though they are red like crimson, they will be like wool.
Isaiah 1:18
For God so loved the world, that He gave His only begotten Son, that whoever believes in Him should not perish, but have eternal life
John 3:16
For I am convinced that neither death, nor life, nor angels, nor principalities, nor things present, nor things to come, nor powers, nor height, nor depth, nor any other created thing, shall be able to separate us from the love of God, which is in Christ Jesus our Lord.
Romans 8:38-39
The life that God gives to those who put their trust in His Christ alone, is not witheld from us until we die. This life begins at the moment we come to Jesus for deliverance from sin, and continues forever and ever. There are specific and supernatural evidences in those to whom God has imparted spiritual life, to authenticate His declaration to sinners in the gospel. These are not a means of gaining or keeping a right standing before God - they are a means of confirming the reality of the fact that God is indeed faithful to save forever all who come, by faith, to Jesus Christ for salvation. These evidences will not all be seen fully or immediately. There is a process of growth in God’s grace, by which He progressively sanctifies those who have become His children. Through these evidences, and through the process of sanctification, God provides a solid assurance that we are His legitimate children.
One of the most prominent evidences of the reality of the fact that God has saved us is that our relationship to sin is radically changed. It is not that we will never sin again, but it is the reality that we will never have the same relationship to sin again. We will never be able to enjoy the passing pleasures of sin the way we used to. We will also experience the discipline of God as our loving and faithful Father if we continue in sinful rebellion, even though we know it is wrong. When God saves us He gives to us a new nature, and we will not be able to ‘practice sin’ as we did before.
Therefore if any man is in Christ, he is a new creature; the old things passed away, behold new things have come.
2 Corinthians 5:17
Little children, let no one deceive you; the one who practices righteousness is righteous, just as He is righteous; the one who practices sin is of the devil; for the devil has sinned from the beginning. The Son of God appeared for this purpose, that He might destroy the works of the devil.
1 John 3:7-8
Another prominent evidence of the reality of God's promise of salvation for all who put their trust in the Lord Jesus is that they will be given a unique, genuine, and enduring love for others who have become children of God in Christ Jesus. This will be a brotherly love that will flow instinctively from a new way of thinking.
Now as to the love of the brethren, you have no need for anyone to write to you, for you yourselves are taught by God to love one another;
1 Thessalonians 4:9
We know that we have passed out of death into life, because we love the brethren. He who does not love abides in death.
1 John 3:14
Another prominent feature of the saving reality God offers to sinners in and through His own Son, is a reverential respect for His Word. This will be evidenced in a genuine hunger for God's Word. And while we will never achieve an absolutely perfect obedience, there will also be an inherent sensitivity in responding to it as it is further understood.
And the seed in the good soil, these are the ones who have heard the word in an honest and good heart, and hold it fast, and bear fruit with perseverance.
Luke 8:15
The one who says, I have come to know Him, and does not keep His commandments, is a liar, and the truth is not in him. But whoever keeps His Word, in him the love of God has truly been perfected. By this we know that we are in Him.
1 John 2:4-5
The best news that could ever be known by sinful men is that there is a God who saves sinners! His promise is certain, and reliable for the present life and all of eternity!
He who has the Son has the life; he who does not have the Son of God does not have the life.
1 John 5:12
Jesus Himself gives us this remarkable and incomparable promise:
. . . he who believes in Me shall live even if he dies.
John 11:25b