St. Thomas Aquinas
“As Christ’s Passion, in virtue whereof this sacrament is accomplished, is indeed the sufficient cause of glory, yet not so that we are thereby forthwith admitted to glory, but we must first ‘suffer with Him in order that we may also be glorified’ afterwards ‘with Him’ (Rom. 8:17), so this sacrament does not at once admit us to glory, but bestows on us the power of coming unto glory. And therefore it is called ‘Viaticum,’ a figure whereof we read in 3 Kings 19:8: ‘Elias ate and drank, and walked in the strength of that food forty days and forty nights unto the mount of God, Horeb.'”
Source: St. Thomas Aquinas, Summa Theologica