John Owen on the Real Effect of Prayer

This passage from the The Holy Spirit: His Gifts and Power is taken from a long section on how the Holy Spirit works within us to effect sanctification. The Holy Spirit prompts us to the spiritual disciplines and to love God more. We pursue the disciplines because we love God, we want to know God better, and we want to be like Him.

For in and by fervent prayer, the habit, frame, and inclinations of the soul to universal holiness, with a detestation and abhorrence of all sin, are increased, cherished, and strengthened. Believers are never raised to a higher intention of spirit in the pursuit of holiness, nor are more conformed to it than in prayer; and hence they often come from it above all impressions from sin, as to inclinations and compliances. Would such a frame always continue, how happy were we! But abiding in the duty, is the best way of reaching out after it. (Owen, pp. 342)

So in summary, pray for holiness and pray for the desire to be holy. If you are weak and we always are, beg for the desire.