We may contrast the communion to which John in the first chapter of his first Epistle, introduces the soul with what Paul gives us at the close of Rom. 8, and also with that which the same apostle gives us at the close of Rom. 11.
In Rom. 1-8 the apostle is instructing us in the secret of peace, which the blood of Christ has provided for the conscience; and, at the end of that scripture, he prepares a triumph for the conscience, or rich exulting communion with God over the work of Christ for His people.
In Rom. 9-11 he is instructing us in the counsels and dispensational wisdom of God; and at the end of that scripture, he prepares a triumph for the delighted and enlarged understanding of the saint, or communion with God over the riches of His wisdom and knowledge.
But in 1 John 1 it is neither of these. It is not communion because of the all-sufficient work of Christ for sinners, or because of the all-glorious and wonderful ways of God. It is communion with Himself, personal communion, because of a well-known relationship between Him and ourselves. This is of another kind, and somewhat of a higher kind.
And we may mark this further.
This last communion to which John introduces us, does not, like the two former, conduct the soul into triumph and exultation, but into calm satisfaction of heart, called “the fullness of joy.” It is rather the exercise of the heart in the sense of personal relationship, not the exercise of the conscience in its assertion of freedom and victory because of the blood of Christ, nor the exercise of the mind, the renewed understanding, in admiring, worshipping delight, because of the treasures of God's revealed wisdom.