William Burkitt on 2 John 1:9

Observe here, 1. The character given of the gospel, it is the doctrine of Christ: that is, the doctrine relating to Christ, and the doctrine taught by Christ.

Observe, 2. What is affirmed of those that apostatize from, and abide not in, the doctrine of Christ, they have not God; that is, say some, they have not God to be their Father, nor the Spirit to be their guide and sanctifier; they have, say others, no knowledge of God, no interest in God, no influences of grace and holiness derived from God.

Observe, 3. The happy condition of those that abide in the doctrine of Christ, they have both the Father and the Son: he that has one, hath both; and he that has not both, has neither: and this having may admit a threefold interpretation, thus; he has the Father and the Son: by way of abode and inhabitation; he dwelleth in God, and God in him; they have the Father and the Son with them by way of society and communion, We will come unto them, and make our abode with them.

Lastly, They have the Father and the Son, by way of assistance and approbation; they have God to assist them, to accept them, to reward them.