The decalogue is the general equity of God's law. Christ summarized the decalogue in the golden rule. The law of nature is substantially identical to the decalogue and was revealed both in Eden and is known naturally by all humans such that all are without excuse before God. The third use of the law, like the first use, is to drive us to Christ. Sanctification is as gracious as justification.
Sanctification is the result of justification.
The Christian life flows from the right use of the means of grace. The latter has been revealed in Holy Scripture and must be known and obeyed. The former is only known ex post facto . There is no secret revelation of God's decretive will. It is more helpful to consider that prayer is the chief part of thankfulness than a means of grace.