There can be no real peace in the heart and mind unless or until there is peace with God respecting sin:
Conscience demands satisfaction or atonement. To this necessity on the side of conscience there are various solutions by our Lord, all of them full of significance. Thus when he invites the weary and Clayton, he plainly eludes the state of an awakened conscience desiring satisfaction or atonement which the individual is not able to offer (Matthew 11:28). The thirsty invited to come and drink are those who are in a similar condition (John 7:37). They who are described in the Sermon on the Mount as hungering and thirsting after righteousness are obviously those who feel the oppression of conscious guilt, and to pay for that a macula “righteousness,” or atonement which alone can fill in satisfy the wants of human nature (Matthew 5:6). Our Lord’s words assumed that such as the harmony between the voice of conscience and the claims of God, or, in other words, between man made in the image of God and the rights of him whose image he bears, that nothing will satisfy conscience that does not satisfy the perfections and law of God. As God’s representative within, it is taken for granted the conscience will quit only when God acquits, and possess peace only when God has opened through the finished redemption. There is an inner or subjective necessity which must come to its rights.
Thus conscience acknowledges that wherever sin is punishment ought to be suffered. We see in the old economy the intense longing of the heart after sacrifices, and the conviction of their insufficiency in the ceremonial law…. And as their holiness group, they would still be haunted by a keener sense of guilt, remembering that they were the same person still, and that no reparation had been made…..
Thus it appears from all history and experience, but conscience is so sensitive, but it will reject everything which made the offer to calm or heal it, till it finds repose in peace and the vicarious death of Christ; and no atonement will avail which is not infinite. Men discover to himself, and aware of his wants, will fall into despair. If the growing sense of guilt is not still by the great redemption of the cross. It is true that mere conscience cannot of itself tell what is an adequate atonement; that it is but a dumb sense of want; and that it often tries false remedies in vain reliefs. The man is a prisoner under guilt, and knows it. God alone knows it provides the adequate atonement; and the unburdened conscience attest to his adequate when found. But no one can persuade conscience that atonement is unnecessary.
–George Smeaton, The Doctrine of the Atonement as Taught by Christ Himself (26-27).
If this is so, then why must believers suffer a lack of peace? Doesn’t the Bible tell us that we must seek peace by prayer (Philippians 4:6-7). Paul says that we pray and God instantly and immediately brings us peace. Isn’t doctrine too abstract? What connection could there be between atonement and peace in the human heart?
Consider more carefully the argument of Paul:
Philippians 4:1–9 (ESV)
1 Therefore, my brothers, whom I love and long for, my joy and crown, stand firm thus in the Lord, my beloved. 2 I entreat Euodia and I entreat Syntyche to agree in the Lord. 3 Yes, I ask you also, true companion, help these women, who have labored side by side with me in the gospel together with Clement and the rest of my fellow workers, whose names are in the book of life.
4 Rejoice in the Lord always; again I will say, rejoice. 5 Let your reasonableness be known to everyone. The Lord is at hand; 6 do not be anxious about anything, but in everything by prayer and supplication with thanksgiving let your requests be made known to God. 7 And the peace of God, which surpasses all understanding, will guard your hearts and your minds in Christ Jesus.
8 Finally, brothers, whatever is true, whatever is honorable, whatever is just, whatever is pure, whatever is lovely, whatever is commendable, if there is any excellence, if there is anything worthy of praise, think about these things. 9 What you have learned and received and heard and seen in me—practice these things, and the God of peace will be with you.
First the problem (vv.1-3): a row in the church. A fight of sufficient intensity that Paul was certain it had survived the trip to bring him news of the quarrel and that it would survive the return of the messenger.
In verse 4, Paul brings up the matter of salvation wrought by atonement (“whose names are in the book of life”). This immediately brings Paul to thoughts of joy (v.5). Paul then moves into a discussion of the relationship with God which includes submission to God in prayer (vv. 5-7).
Paul then moves to the matter of meditation and conduct (vv. 8-9). In the meditation list, what could Paul possibly have considered relevant for such meditation? In Philippians 2:5 Paul tells them to have or better that they already have the condition and basis to think like Jesus: “Adopt then this frame of mind in your community – which indeed is proper for those who are in Christ Jesus” (Moises Silva, translation). The content of that meditation in Philippians 2 is the work of Jesus in humiliation, death and resurrection to glory, i.e., the atonement.
We remain too much without peace, because we recall too infrequently how great a glory and how deep a hope we have in Jesus. We fail to see the greatness of the atonement, and thus we wallow in anxiety. Believer, drink deeply from the hope and joy of the atonement – and you will not be troubled. Do not turn your eyes from your hope.