Some helpful thoughts taken from chapter 22 of Herman Bavinck’s Our Reasonable Faith (Eerdmans, 1956). Italics mine:

Page 474: “In justification we are declared free of guilt and punishment on the basis of a righteousness which is outside of us in Christ Jesus, and which through God’s grace is reckoned to us and on our own part is received in faith. In sanctification, however, the holiness of Christ is most certainly poured out in us through the Holy Spirit. When Roman Catholicism therefore speaks of a grace which is poured into us, we have no objection to that in itself; we object only to the fact that this grace is regarded as a part of the righteousness on the basis of which we are declared free before God. For, if that were so, then justification and sanctification, the deliverance from guilt and the removal of the pollution, would be confused with each other; and then Christ would be robbed of the perfection of His achieved righteousness and the believing soul of its comfort and assurance.”

Page 510—511: “The assurance of salvation is not something which is added to the life of faith from without, but something, rather, which blossoms up out of that life of faith itself. Hence, the assurance differs according to the measure of the faith… But all this does not take away from the fact that the saving faith, such as Scripture describes it and the Reformation restored it, is not in its inner nature certainty, and that this certainty becomes stronger in proportion to the extent that the faith becomes stronger. Such faith is not opposed to knowledge, but it is opposed to all doubt whatsoever. Doubt does not come up out of the new man but out of the old; it does not come up out of the Spirit but out of the flesh. The faith says yea and amen to all the promises of God, embraces those promises, and leans upon them. As it does this, and in proportion to the extent that it does so, the refugee confidence of the faith becomes sure confidence, and it gives the believer the freedom to apply all of those promises of God to himself and to appropriate them; the growing confidence becomes a sure confidence that not to others only but to me also the forgiveness of sins, eternal righteousness and salvation have been given of God, out of pure grace, and solely for the merits of Christ.”

Pages 512—513: “But we must carefully note that in seeking for assurance we cannot begin with these good works, that the faith can never firmly lean or rest upon them, and that still less can they be performed by us with a view to our achieving the assurance of salvation by means of them. For all good works are imperfect, and they are more or less perfect in proportion to the extent that they issue from a stronger or weaker faith. But to the extent that they do issue from a true faith, they can serve as aids to our assurance. Just as faith proves and illustrates itself in good works, so the faith is also confirmed and strengthened by them.”