It seems to me that Christians find most if not all of their Christian comfort from the fact that the Lord Jesus has forgiven them their sins. But complete comfort comes from not only being justified before God, free from the guilt and pollution of our sin by Christ, but also comes from obedience to the commands of God, in Christian graces existing in our hearts and acted out, and mortification of the carnal man, in a sanctified life.
Christ bought sanctification through His atonement, and thus, it is required for the full effect of Christ’s work for us in our Christian lives.
We can draw comfort from the propitiation for our sin, and it seems to me many do, but complete comfort must also include a sanctified, holy life.
I would suggest that, a person who believes they are Christian but does not have the desire for, nor the evidence of, the sanctification process in their life, does not have grounds for Christian comfort.
The following is from Puritan Thomas Manton regarding this topic, in volume 18 of his works, in a sermon on Acts 10:34-35:
True; but though it be in us, it is not of us. It floweth from the same grace of God, and the same power and merit of the Lord
Jesus. And something there must be in us, or how shall we make out our title and claim, or know that the grace of God belongeth to us? If we look only to justification, and suspect all comfort that is elsewhere derived, we are in danger of falling into the gross part of the error of Poquinus and Quintinus, who in Calvin’s time asserted it to be the only mortification to extinguish the sense of sin in the heart. But this is not to mortify sin, but to mortify repentance and holiness, to crucify the new man rather than the old, not to quiet conscience, but outface it. Surely where there is sin there will be trouble. Sanctification is one means of applying the grace of God, as well as justification; and we must look to both benefits, and the mutual respect they have to one another.
But because this prejudice is drunk in by many not ill-meaning people, let us a little dispossess them of this vain conceit.
(2.) It is as true that ‘whosoever is in Christ, he is a new creature’, 2 Cor. v.. 17. So that the dispute will lie here; to clear up our interest in Christ, whether we are new creatures; for till that be determined, we can have no solid peace and comfort within ourselves,
(3.) None is a new creature but he who feareth God and worketh righteousness; for that is the description of a new creature, that all old things are passed away, and all things are become new; a new heart, a new mind, and a new conversation [behavior]; for a new heart is only sensibly discovered by newness of life, Rom. vi. 4. Well, then, our proposition is fully reconcilable with the grace of Jesus Christ.
[3.] With respect to the Spirit, who is our sanctifier and comforter. First a sanctifier, and then a comforter, and therefore a comforter because a sanctifier. Otherwise the Spirit would cause us to rejoice we know not why, and the comforts of a christian would be fantastical and groundless; at best we should rejoice in a mere possible salvation. But holiness is God’s seal and impress upon us: Eph. i. 13, ‘In whom also, after that ye believed, ye were sealed with that Holy Spirit of promise.’
When his sanctifying work is interrupted, so is his comforting work disturbed also, Eph. iv. 31. David’s bones were broken, and he lost his joy, when he fell into great sins, Ps. li., and Ps. xxxii. And it is true in others, who, when they have been lifted up to heaven in comfort, have fallen almost as low as hell in sorrow, trouble, and perplexity of spirit, when they grew remiss, negligent, and disobedient to the motions of the Holy Ghost. If we intermit a course of holiness, the frowns of God will soon turn our day into night; and the poor forsaken soul, that was feasted with the love of God, knows not whence to fetch the least support. Such is the fruit of our careless and loose walking.
May God sanctify us by His Spirit because of Christ; may He grant us a desire to be obedient and live holy lives, including obedience to His commands in living out the graces of His Spirit and mortification of the carnal man and a putting away of things in this world that feed it; and may we diligently ask Him for these things to be put in our hearts.