Romans 8:9–10 — However, you are not in the flesh but in the Spirit, if indeed the Spirit of God dwells in you. But if anyone does not have the Spirit of Christ, he does not belong to Him. 10 If Christ is in you, though the body is dead because of sin, yet the spirit is alive because of righteousness.
Ephesians 3:16–17 — that He would grant you, according to the riches of His glory, to be strengthened with power through His Spirit in the inner man, 17 so that Christ may dwell in your hearts through faith; and that you, being rooted and grounded in love,
We have seen that baptism proclaims the union between Christ and the believer, and that this union is Legal, Federal and vital in nature. This time we will dwell on the fact that it is also a spiritual union, by which we mean that it is brought about and sustained through the agency of the Holy Spirit.
It is the Holy Spirit's work to join someone to Christ, as we have seen, and in that joining, Christ Himself takes up residence in the heart of the new believer through His Spirit. So critical is this truth that Paul declares in our first text above that someone is not a Christian - does not belong to Christ - unless they have the Spirit dwelling in them. The Spirit is the one Who breathes new life into the believer's spirit, bringing about a distinction from the body which remains dead because of sin.
In our second text, Paul tells us that the Holy Spirit is the One Who continues this work in believers, giving power to strengthen them inwardly so that Christ may dwell in them by faith. In other words, the Spirit initiates but then maintains this work and this influence in their lives.
So we need to reflect on this in connection with our baptism and when we witness the baptism of others. We see the washing of water and understand that this speaks of the cleansing activity of the Spirit as He applies the work of Christ to an individual. But we can go further in our reflection and think about the indwelling of God's Spirit that begins at that time, as we are joined to Christ, and we can also consider how that indwelling continues and should grow in all believers, taking them deeper into Christ in terms of their understanding, love and likeness to Christ.
In closing, we must ask the reader whether they "have the Spirit of Christ," as Paul puts it above, without Whom they are still dead in trespasses and sins.