For The saying is sure see 1 Tim 1.15.

We here and in the rest of the hymn is inclusive, referring to all Christians. Him refers to Christ; in many cases it may be necessary to make this information explicit in the translation. Have died with translates a rare verb (in addition to this verse it occurs twice elsewhere in the New Testament, namely in Mark 14.31 and 2 Cor 7.3). The verb here is in the aorist tense, indicating that a definite completed past event is being referred to. Since we are actually alive, this argues against interpreting death here in a physical sense, which some interpreters have suggested. It is more likely that death here is used in a figurative sense, referring to the death of the old self when one comes to trust in Christ Jesus. In the New Testament this death is sometimes symbolized by the sacrament of baptism (see especially Rom 6.3-8); this is perhaps what is intended here as well. But translators should maintain the ambiguity. With here and in what follows expresses the idea of being in company with, and is used figuratively to express being in fellowship with Christ.

Live with also translates a very rare verb (in addition to this verse it occurs in Rom 6.8 and 2 Cor 7.3). The future tense of the verb suggests much more than experiencing fellowship with Christ in the present; it in fact recalls verse 10, that is, the experience of eternal glory in the presence of Christ.

Quoted with permission from Arichea, Daniel C. and Hatton, Howard A. A Handbook on Paul’s Second Letter to Timothy. (UBS Handbook Series). New York: UBS, 1995. For this and other handbooks for translators see here .