Sexual intercourse engaged in outside of the marriage relationship is forbidden by the Scriptures and must be condemned by the church. God says:
“Therefore a man shall leave his father and his mother and hold fast to his wife, and they shall become one flesh” (Genesis 2:24).
“For you know what instructions we gave you through the Lord Jesus. For this is the will of God, your sanctification: that you abstain from sexual immorality; that each one of you know how to control his own body in holiness and honor, not in the passion of lust like the Gentiles who do not know God” (1 Thessalonians 4:2-5).
“Now the works of the flesh are evident: sexual immorality, impurity, sensuality” (Galatians 5:19).
“But sexual immorality and all impurity or covetousness must not even be named among you, as is proper among saints” (Ephesians 5:3).
“Put to death therefore what is earthly in you: sexual immorality, impurity, passion, evil desire, and covetousness, which is idolatry” (Colossians 3:5).
“Or do you not know that he who is joined to a prostitute becomes one body with her? For, as it is written, ‘The two will become one flesh.’ But he who is joined to the Lord becomes one spirit with him. Flee from sexual immorality. Every other sin a person commits is outside the body, but the sexually immoral person sins against his own body. Or do you not know that your body is a temple of the Holy Spirit within you, whom you have from God? You are not your own, for you were bought with a price. So glorify God in your body” (1 Corinthians 6:16-20).
Even when the partners feel themselves united by a deep bond of love and intend to be married at some point in the future, such as in “engagement”, the same judgment must be made.
The Bible also clearly teaches, of course, that there is full and free forgiveness for all who repent of their sins and put their trust in God's Son, Jesus Christ (Rom. 8:1; 1 John 1:8-9).
While Scripture teaches, secondly, that all children born into this world (regardless of the circumstances of their conception) are by nature sinful and unclean (Psalm 51:5), God has provided a way (through Holy Baptism) for children to be cleansed from sin and forgiven. God also makes it clear in His Word that all children are precious and highly valued in His sight and are to be regarded as a blessing (Psalm 127; Matt. 19:14).