One of the core beliefs of Christianity (see Sections 1.3, 13.19 and 13.20 of Theology Corner) can be stated as:
Salvation from the consequences of sin is offered to all persons by the grace of God and the substitutionary atonement of Jesus Christ (Deut 10:17; 2 Chron 19:7; Job 34:18-19; Lam 3:33; Ezek 18:23-25, 33:11; Mark 12:14; John 1:29, 3:16, 14:6; Acts 4:10-12, 10:34-35; Rom 2:11, 3:21-25, 5:12-18; Eph 2:8-10, 6:9; 1 Tim 2:3-5, 4:9-10; Heb 9:14-15; 2 Pet 3:9; 1 John 2:2).
The grace of God by which we are saved is called Prevenient Grace or the grace that comes before salvation (see Sections 4.2, 4.9 and 4.10 of Theology Corner). Remember, justice is getting what you deserve. Mercy is not getting what you deserve. Grace is getting a completely undeserved and unimaginable gift from God.
The substitutionary atonement is an indestructible thread woven throughout the fabric of this website and throughout Christian Theology in general. Here are some words of Samuel Wakefield on these issues showing how only the substitutionary atonement could satisfy the character and government of God.
"How then can mercy be extended to our guilty race consistent with the character and government of God and with the highest interests of his moral creatures? The only answer is found in the Holy Scriptures. They alone show, and indeed they alone profess to show, how God may be just, and yet the justifier of the ungodly. Other schemes show how he may be merciful; but the difficulty lies not there. This meets it by declaring the “righteousness of God,” at the same time that it proclaims his mercy. The voluntary sufferings of an incarnate Divine person “for us” in our room and stead, magnify the justice of God, display his hatred to sin, proclaim the “exceeding sinfulness” of transgression by the deep and painful agonies of the Substitute, warn the persevering offender of the terribleness and certainty of his punishment, and open the gates of salvation to every true penitent.
The same Divine plan secures the influence of the Holy Spirit to awaken the wanderer to repentance and lead him back to God; to renew his fallen nature in righteousness at the moment he is justified through faith, and to qualify him to “walk not after the flesh, but after the Spirit.” All the ends of government are here answered. No license is given to sin, the moral law is unrepealed, the day of judgment is still appointed, future and eternal punishments still display their awful sanctions, a new and singular manifestation of the Divine purity is afforded, pardon is offered to all who seek it, and the whole world may be saved!
With such evidence of suitableness to the case of mankind, and under such lofty views of connection with the principles and ends of moral government, does the doctrine of THE ATONEMENT present itself. But other important considerations are not wanting to mark the united wisdom and goodness of this method of extending mercy to the guilty. All that can most powerfully illustrate the united tenderness and awful majesty of God, and the odiousness and destructive tendency of sin; all that can win back the heart of man to his Maker and Lord, and render future obedience a matter of affection and delight as well as duty; all that can extinguish the angry and malignant passions of man toward man; all that can inspire a mutual benevolence, and dispose to a self-denying charity for the benefit of others; and all that can arouse by hope, or tranquilize by faith, may be found in the vicarious death of Christ, and in the principles and purposes for which it was endured." (Wakefield, p 103-104)
(See also Sections 1.4, 1.5, 1.24, 11.7 and 12.9 of Theology Corner)