Jesus defines discipleship as following him (Lk 9:23), a concept Luke develops above all by noting the presence of the disciples continually “with” Jesus (Lk 6:17; 7:11; 8:1; 9:10; 22:22.214.171.124; cf. Lk 8:38; 22:33). This may seem a rather vague and passive role, this “being with Jesus”, but in Acts it becomes one of the key credentials for the apostolic office (Acts 1:21). Being with Jesus suggests companionship with Jesus, sharing in his success and failure, his acceptance and rejection; it entails identifying with and being shaped by Jesus’ own life and mission.
In Luke 9:43, following Jesus is understood in the context of self-denial and daily cross-bearing. On the one hand, Luke seems to have in mind some form of impending persecution of Jesus’ followers – hence, the emphasis on public denial of oneself rather than of one’s faith in Jesus (cf. 9:24-26; 12:8-12). On the other, the threat of execution is apparently not present; after all, Luke’s emphasis on daily cross-bearing precludes a literal understanding of “cross-bearing” as preparation for one’s own crucifixion.
Set within the context of Jesus’ journey to Jerusalem, this cross-bearing must mean embracing and serving in a single-minded way (setting one’s face to, 9:51) the redemptive purpose of God. (From Joel B. Green, The Theology of the Gospel of Luke, Cambridge University Press 1995, pp. 108-109)