And because the number of the saints is gathered by no preceding merits, as was said, but only by the gratuitous will of God concerning such, correctly John, about to write to the seven churches which are located in Asia, puts forth the heading of his greeting, saying: Grace to you and peace from him who is, and who was, and who is to come, and from the seven spirits who are before his throne, and from Jesus Christ (Rev. 1:4-5). For, grace is said to be something that has been given freely, not something paid as a reward, but something conferred freely through kindness. For, when this grace shined within us, we, from enemies were led back to friendship with our Creator, from ungodly were made godly, and from servants of sin were adopted as children of righteousness. Every day we are illuminated by this preceding grace so that we may be able to see where we should place our step regarding good work. We are guarded by subsequent grace so that in the end we are not bitten by a serpent in the heel. By this grace we are incited to good work, but having been incited, unless that grace supports what it has incited, we are unable to complete that same work. On this Paul says: The will is present with me, but to do good I do not find (Rom. 7:18). Accordingly, therefore, the will that is present with you, is only because you received it by grace, as you yourself said in another passage: What do you have that you did not receive? (1 Cor. 4:7) Therefore, just as the will was present with Paul because he received this very thing by grace, so he did not find it to do good unless that very grace, which gave him the will, supported it. Accordingly also, the same Apostle says again: It is God who works in you both to will and to do his good pleasure (Phil. 2:13). For, John, Peter, and Paul, when they were about to write to believers, put forth this grace in the heading of their greetings in their writings.
Ambrose Autpert (730-784), Expositio in Apocalypsin. On Rev 1:3-5.