Thoughts of Grace

Ephesians 6:18
Praying always with all prayer and supplication in the Spirit,
and watching thereunto with all perseverance and supplication for all saints;

Praying refers to the state of the spirit as well as to the act.

With all prayer – Refers to the different kinds of prayer that is performed in public, in the family, in the closet, in business, on the way, in the heart without a voice, and with the voice from the heart. All those are necessary to the genuine Christian; and he whose heart is right with God will be frequent in the whole. “Some there are who use only mental prayer or ejaculations, and think they are in a state of grace, and use a way of worship far superior to any other; but such only fancy themselves to be above what is really above them; it requiring far more grace to be enabled to pour out a fervent and continued prayer, than to offer up mental aspirations.” Rev. J. Wesley.

And supplication – There is a difference between prayer, and supplication. Some think the former means prayer for the attainment of good; the latter, prayer for averting evil. Supplication however seems to mean prayer continued in, strong and incessant pleadings, till the evil is averted, or the good communicated.

There are two things that must be attended to in prayer.
1. That it be in every time, season, or opportunity;
2. That it should be in or through the Spirit – that the heart should be engaged in it, and that its infirmities should be helped by the Holy Ghost,

Watching thereunto – Being always on your guard lest your enemies should surprise you. Watch, not only against evil, but also for opportunities to do good, and for opportunities to receive good. Without watchfulness, prayer and all the spiritual armor will be ineffectual.

With all perseverance – Being always intent on your object, and never losing sight of your danger, or of your interest. The word implies stretching out the neck, and looking about, in order to discern an enemy at a distance.
Clarke’s Commentary, edited