In a chapter on Christ and Government, Penington cautions against a "lofty ruling spirit, which loves to be great, which loves to have dominion, which would exalt itself, because of the gift it has received, and would bring others into subjection". I really love this phrasing:
For it is not so much speaking true things that doth good, as speaking them from the pure, and conveying them to the pure: for the life runs along from the vessel of life in one, into the vessel of life in another; and the words (though ever so true) cannot convey life to another, but as the living vessel opens in the one, and is opened in the other.
I take this as saying that it isn't the words themselves that are important, but speaking them from the Spirit.
Later in the same chapter, he talks about not believing particular truths just because others see them, or doing various practices just because you see others do them:
Therefore the main thing in religion is to keep the conscience pure to the Lord, to know the guide, to follow the guide, to receive from him the light whereby I am to walk; and not to take things for truths because others see them to be truths; but to wait till the Spirit make them manifest to me; nor to run into worships, duties, performances, or practices, because others are led thither; but to wait till the Spirit lead me thither.
He also cautions against judging others in their spiritual practices:
Even in the apostles' days, Christians were too apt to strive after a wrong unity and uniformity in outward practices and observations, and to judge one another unrighteously in these things. And mark; it is not the different practice from one another that breaks the peace and unity, but the judging of one another because of different practices. He that keeps not a day may unite in the same Spirit, in the same life, in the same love with him that keeps a day; and he who keeps a day, may unite in heart and soul with the same Spirit and life in him who keeps not a day; but he that judgeth the other because of either of these, errs from the Spirit, from the love, from the life, and so breaks the bond of unity.
And here is the true unity in the Spirit, in the inward life, and not in an outward uniformity.
While we may think of that "outward uniformity" as referring to programmed worship or outward sacraments, I believe it applies just as well to our unprogrammed worship. Sitting in silence can be just as much an "outward uniformity" if all we are doing as a group is sitting in silence. It is the communal seeking and experience of the Spirit that is the heart of unprogrammed worship. The silence is merely our assent to be guided by God.