For if we have been planted together - The word used here σύμφυτος sumphutos, does not occur elsewhere in the New Testament. It properly means sown or planted at the same time; what sprouts or springs up together; and is applied to plants and trees that are planted at the same time, and that sprout and grow together. Thus, the name would be given to a field of grain that was sown at the same time, and where the grain sprung up and grew simultaneously. Hence, it means intimately connected, or joined together. And here it denotes that Christians and the Saviour have been united intimately in regard to death; as he died and was laid in the grave, so have they by profession died to sin. And it is therefore natural to expect, that, like grain sown at the same time, they should grow up in a similar manner, and resemble each other.
We shall be also - We shall be also fellow-plants; that is, we shall resemble him in regard to the resurrection. As he rose from the grave, so shall we rise from sin. As he lived a new life, being raised up, so shall we live a new life. The propriety of this figure is drawn from the doctrine often referred to in the New Testament, of a union between Christ and his people. See this explained in the notes at John 15:1-10. The sentiment here inferred is but an illustration of what was said by the Saviour John 14:19, “Because I live, ye shall live also.” There is perhaps not to be found a more beautiful illustration than that employed here by the apostle of seed sown together in the earth, sprouting together, growing together, and ripening together for the harvest. Thus, the Saviour and his people are united together in his death, start up to life together in his resurrection, and are preparing together for the same harvest of glory in the heavens.
In the likeness of his resurrection - This does not mean that we shall resemble him when we are raised up at the last day - which may be, however, true - but that our rising from sin will resemble his resurrection from the grave. As he rose from the tomb and lived, so shall we rise from sin and live a new life.