What is the main teaching of the Bible?
“All have sinned and fall short of the glory of God” - Romans 3:23
Every one of us has sinned against God. This sin comes with a cost.
“For the wages of sin is death” - Romans 6:23
Our sin has caused our spiritual death before God. It is the just wages for our sin, and the cost is our eternal separation from God, “But your iniquities have made a separation between you and your God, and your sins have hidden His face from you so that He does not hear,” Isaiah 59:2.
“But God demonstrates His own love toward us, in that while we were yet sinners, Christ died for us” - Romans 5:8
Even though we were in this lost state, and had no way of ourselves to be saved, even so, God has provided the way.
“For Christ also died for sins once for all, the just for the unjust, so that He might bring us to God, having been put to death in the flesh, but made alive in the spirit,” and, “He Himself bore our sins in His body on the cross, so that we might die to sin and live to righteousness; for by His wounds you were healed” - 1 Peter 3:18, 1 Peter 2:24
God has provided the sacrifice for our sins, Christ has paid the cost of our redemption. But something is still required of man in order for him to be saved, for, “Not everyone who says to Me, ‘Lord, Lord,’ will enter the kingdom of heaven, but he who does the will of My Father who is in heaven will enter,” Matthew 7:21
What is required of us to be saved? First, we must hear and believe the gospel,
“Truly, truly, I say to you, he who hears My word, and believes Him who sent Me, has eternal life, and does not come into judgment, but has passed out of death into life,” John 5:24
“Therefore I said to you that you will die in your sins; for unless you believe that I am He, you will die in your sins,” John 8:24
We must confess Him before men,
“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,” Romans 10:9
We must repent of our sins,
“I tell you, no, but unless you repent, you will all likewise perish,” Luke 13:3
And we must be baptized,
“Repent, and each of you be baptized in the name of Jesus Christ for the forgiveness of your sins; and you will receive the gift of the Holy Spirit,” Acts 2:38
For,
“He who has believed and has been baptized shall be saved; but he who has disbelieved shall be condemned,” Mark 16:16