1 John 2:24

Let that therefore abide in you
Meaning the word of God, ( 1 John 2:14 ) ; the Gospel of Christ, which there was reason to believe had a place in their hearts, and which they had embraced and professed; and therefore the apostle exhorts them to perseverance in it; and particularly not to let go the doctrine concerning the Father and the Son, and this their relation to each other, which is the foundation of the doctrine of the Trinity, and of the distinct personality of Father, Son, and Spirit; the contrary to which leaves the three without either name, or distinction from each other: the arguments to enforce this exhortation follow,

which ye have heard from the beginning;
they had heard it not externally only, but internally; they had hearkened to it, and from the heart obeyed it; they had mixed it with faith, and received the love of it; they had heard it from the apostles of Christ, who were eye and ear witnesses of the word; and this they had heard at the first preaching of the Gospel to them, at the first of their conversion: the apostles of Christ began their ministry with the sonship of Christ, and greatly insisted on it, in it, and required a profession of it before baptism, and which was made in order to it; and these believers had been baptized in the name of the Father, and of the Son, as standing in such a relation to each other; see ( Acts 9:20 ) ( 8:37 ) ( Matthew 28:19 ) ; and therefore ought not to relinquish this truth, and receive a new and upstart notion: and for further encouragement to continue in it, it is added,

if that which ye have heard from the beginning shall remain in you,
ye also shall continue in the Son, and in the Father;
as those that are once in either always will; what is here said is not either the cause or condition of men being in the Father, and in the Son, or of their continuance in them, but is descriptive of the persons that are in them, and is an open and manifest evidence of their being and continuance in them. Such are in union with Christ, and at times enjoy sensible communion with him, and shall never be finally and totally removed from it; they are in the love of Christ, from whence there is no separations, and in the arms and hands of Christ, out of which none can pluck them; and they abide by him in the exercise of faith and love, and cleave unto him with full purpose of heart, and will hold on and out, professing his name to the end: and they are, and abide in the love of God the Father, which is from everlasting to everlasting; and in the covenant of his grace, which is sure and inviolable; and in the participation of all the blessings and promises of it, among which, the following one, eternal life, is a principal one.