The phrase “eternal life” is well known for its frequent use throughout the NT. Paul uses the phrase regularly (4x in Romans, 2x in 1 Tim, 2x in Titus), but the only place he mentions it in Galatians is 6:8:
For the one who sows to his own flesh from his flesh will reap corruption, but the one who sows to the Spirit from the Spirit will reap eternal life.
Given the singular use within the book and the likely order of Galatians as the earliest Pauline epistle, it is worth taking a closer look within the context to determine what Paul intended with the phrase. Neither the adjective αἰώνιος “eternal” nor the noun ζωή “life” occur elsewhere in Galatians, but cognate words do. The noun αἰών “age” occurs in Gal 1:4, 5, with present and future reference. Paul speaks of believers’ rescue from ἐκ τοῦ αἰῶνος τοῦ ἐνεστῶτος πονηροῦ, “this present evil age,” on the one hand, and on the other hand he speaks of glory to God εἰς τοὺς αἰῶνας τῶν αἰώνων, “to the ages of the ages,” a future-looking reference. The adjective αἰώνιος “eternal” shows similar flexibility in its temporal reference. Although normally interpreted as future, it can have a past reference; see for example Rom 16:25; 2 Tim 1:9; Titus 1:2. This shows that the adjective takes on in addition to the temporal reference of its root a sense of quality, “without end.” Within the book the adjective invokes the same eschatological context which αἰών “age” does in the introduction to the book: God is at work within the present age to secure believers’ place in the next. Related to the noun ζωή “life” is the verb ζάω “to live,” which Paul uses frequently within Galatians. One use is mundane (Gal 2:14), but the remaining uses are fraught with theological meaning. Within the theological crux of the book Paul speaks of living to God (2:19) and of living his present life through faith in Christ (2:20). In 3:11 and 12 Paul cites Hab 2:4 and Lev 18:5, both of which use ζάω significantly to describe living as a result of proper orientation to God. Lastly, Paul speaks in 5:25 of living by the Spirit, perhaps the key reference for understanding the present context given his focus on the Spirit. Life within Galatians is not simply living; rather it is living to God by faith in Christ through the means of the Spirit. Paul’s argument in the present paragraph focuses directly upon the role of the Spirit in that process. A believer’s sowing to the Spirit, in context defined as acceptance of and obedience to Paul’s gospel which properly understands the role of the Spirit in the present time—enables the Spirit in return to give the blessing of an life enabled before God in Christ which spans the gap between the present age and the age to come.