How Do We Know We are Filled With the Holy Spirit?

How shall a person know, since the modes of the Spirit's interior action are so various, when he experiences the full or completed presence and operations of this Divine Agent? A proper answer, so far as it goes, would perhaps be, that this can be known only by the results of such divine presence and agency. These results, in their entire length and breadth, we will not attempt to analyze at the present time. But will only go so far now as to say, that one of the most decisive marks of the presence of the Holy Ghost in its fullness, is a resigned and peaceful state of the spirit originating in perfect faith in God. In the precise state of mind to which we now have reference, there seems to be an entire subsidence or withdrawal of that natural excitability which is so troublesome to the christian; and instead of the eager and unsettled activity of nature, the substitution of a pure and deeply interior rest of the soul, such as was seen in our Savior, and resembling, on the small scale of man's limited spirituality, the sublime and  passionless  tranquility of God.

Undoubtedly there are other important marks, characteristic of the inward fullness of the divine power. But this, if it be rightly understood, may be regarded as the highest result of the divine operation upon the human mind. It is not, therefore, merely the christian, whose mental exercises are characterized by traits, that are calculated to excite outward observation that is filled with the Holy Ghost, to the exclusion of others. Still more frequently is this fullness experienced in the hearts of those who sit in solitary places, unknown to the world; who live in the secrecy of their spirits with God alone; and of whom the multitude around them, ignorant of the interior Power which dwells in their souls, know only this, that they perform the religious and temporal duties of life with fidelity and gratitude, and endure its trials and sorrows with silence and submission. We would not have it understood, however, as these remarks might seem to imply, that persons in this calmly peaceful and triumphant state of mind, are destitute of feeling. Far from it. They have feeling; but it is regulated feeling. Perfect in degree, but symmetrical in all its relations; and therefore resulting in that angelic aspect of religious experience, which has been indicated. And the explanation is this. Every emotion is so perfectly adapted to its appropriate object; every desire and affection is kept so perfectly in its position; every volition moves so surely and strongly towards the goal of perfect rectitude; all worldly tendencies and attachments, all hopes and fears, all joys and sorrows are so completely merged in the overruling principle of supreme love to God, a principle which makes all of God and nothing of the creature, that the result is, and of necessity must be, inward quietude;

"The peaceful calm within the breast,

"The dearest pledge of glorious rest."

— edited from The Interior or Hidden Life (2nd Edition, 1844) Part 3, Chapter 1.