Elena,
When asked this question I typically respond with a question of my own. The question is: what do you confess?
1. Do you confess that Jesus Christ is the Son of God? (Matt. 16:16)
2. Do you confess that you are a sinner and have transgressed God's law? (Rom. 3:23)
3. Do you confess that, as a sinner, you deserve death and judgment? (Rom. 1:18; 6:23a)
4. Do you believe that Jesus Christ died to pay the penalty for your sin? (2 Cor. 5:21)
5. Do you believe that Jesus Christ rose from the dead and defeated sin? (1 Cor. 15:3, 4)
6. Have you turned from your sin (repentance) and believed (by faith) in the finished work of Jesus Christ on your behalf? (Eph. 1:13, 14)
7. Do you confess a desire to serve God actively in the church by loving the saints and doing good works? (Eph, 2:10; Phil. 2:12)
A Christian does not do any of these things perfectly. We sin, fall down, repent, and are restored, and then do it all over again. We are in the process of being perfected in our behavior, we are not perfected in our behavior yet. But the first step is to be honest in what we confess before God.
Romans 10:9, 10 9 that if you confess with your mouth Jesus as Lord, and believe in your heart that God raised Him from the dead, you will be saved;10 for with the heart a person believes, resulting in righteousness, and with the mouth he confesses, resulting in salvation.
One knows that they are saved if they have trusted Jesus Christ as their Savior.
1Jn 5:12 He that hath the Son hath life; and he that hath not the Son of God hath not life.
We have all sinned. We have broken God's law. God demands absolute holiness, something one cannot attain by one's own merit. There is nothing that one can do to earn eternal life or to merit entrance into heaven.
The Bible says:
Rom 6:23 For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord.
--A wage is something I deserve. I deserve to get paid at the end of the day. That is my wage. But here I deserve death--spiritual death or separation from God for all eternity.
The gift of God is eternal life but the wages of sin is eternal death. (separation from God).
This is the reason Christ came--to pay the penalty that I could not pay, that is to die for my sins.
He paid the penalty that God demanded. His blood was sufficient to pay for our sins.
He died on the cross to make an atonement for our sins, to pay a penalty I could never pay.
He could do this for two reasons: 1. Christ is and was, and always will be God. Only God can pay the penalty of all our sins. And, 2, because he was perfect man. He never sinned. God required a sinless sacrifice.
1Pe 3:18 For Christ also hath once suffered for sins, the just for the unjust, that he might bring us to God, being put to death in the flesh, but quickened by the Spirit:
--He is the Just one that suffered and died for the unjust ones, (us), that he might bring us to God.
He was put to death but made alive by the Holy Spirit. He died, was buried and rose again.
On that basis, if one trusts him as his Savior he can be saved.
The Scriptures say:
Rom 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.
Rom 10:10 For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation.
--Belief comes from the heart. It is not simple head knowledge. Believe from your heart that Christ is Lord. It is Him you must ask to save you.
Joh 1:12 But as many as received him, to them gave he power to become the sons of God, even to them that believe on his name:
--As many as received him to them gave he power to become the sons of God...
1Jn 5:13 These things have I written unto you that believe on the name of the Son of God; that ye may know that ye have eternal life, and that ye may believe on the name of the Son of God.
---Now John says after you have believed on the name of the Son of God, you may
know you have eternal life.
Why? Because you have believed on the name of the Son of God.
We know because we have believed. We trust in the promises of God through faith.