John Wesley on Romans 4:15

Because the law - Considered apart from that grace, which though it was in fact mingled with it, yet is no part of the legal dispensation, is so difficult, and we so weak and sinful, that, instead of bringing us a blessing, it only worketh wrath; it becomes to us an occasion of wrath, and exposes us to punishment as transgressors. Where there is no law in force, there can be no transgression of it.