He was crucified: the verb used here does not occur elsewhere in this letter. It is frequent in the Gospels and is found four times in (1 Corinthians 1.13, 23; 2.2, 8). It involves putting a person to death by nailing him to a cross. The passive form will have to be made active in many languages. Translators may say “people killed him by nailing him to a cross” or, leaving certain information implicit, simply “he died on the cross.”
In weakness refers to the weakness of Christ’s human nature, that is, he was weak because he was a human being. Some languages may speak of “lacking strength in his body.”
Christ lives by the power of God, meaning that God showed his power in raising Christ from the dead (see Rom 1.4). The whole first half of this verse may read “It is true that he lacked strength when they attached him to the cross, but he now lives by the power of God.”
The sense of the second half of the verse is that, when Paul comes to Corinth, weak as he may appear to be, he will be in fellowship with the risen Christ and will share God’s power in his dealings with the Corinthian church.
The pronoun we in this verse is exclusive, that is, the readers are not included. Since Paul uses the first person singular pronoun in verses 1-3, it is not clear whether the change to first person plural (we) is a stylistic change only or whether he intends to include his co-workers also. If translators decide that Paul is using the epistolary plural (see comments on 1.1 and on page 5), they may wish to use the pronoun “I” instead of “we” (so Nueva Biblia Española) here and in verses 6 and 7.
In dealing with you: or, more literally, “toward you,” which in Greek stands in contrast with in him. Anchor Bible attempts to reflect this contrast as follows: “we are weak in him, but toward you we shall live with him by the power of God.” However, it may be unnatural to try to do this in other languages. The meaning is “we are weak just as Christ was, but you will see that we will live by the power of God, just as Christ does.”
The words we shall live with him do not here refer to the future life after death but to Paul’s present fellowship with the risen Christ. It will perhaps be necessary to say something like “we shall go on living with him.”
Quoted with permission from Omanson, Roger L. and Ellingworth, Paul. A Handbook on Paul’s Second Letter to the Corinthians. (UBS Handbook Series). New York: UBS, 1993. For this and other handbooks for translators see here .