"A.B.C." or "just love Jesus" may be a good start (though "just loving Jesus" omits our sin and the Gospel's command to "repent"), but we are not obeying the Great Commission with these things alone. There is a "teaching" that is involved that never ends. This "teaching" does not start with our "felt needs" or "life situation" or us at all, but with the One Who "has been given...all authority...in heaven and on earth." He is Commander, there are commands, and we are to be the commanded. This is the fullness of obedience to the Great Commission. It starts with knowledge of God and His will for His servants.
Despise not theology, beloved. Jesus Himself, in His "high priestly prayer" in John 17, identifies theology as the key to eternal life: "This is eternal life, that they may know You [theology], the only true God, and Jesus Christ Whom You have sent" (17:3). The fullness of evangelism and obedience to the Great Commission goes far beyond a bare and basic confession. It continues to be taught and grows in knowledge of the Father and Son through the instruction of the Holy Spirit, Who teaches in and through His Church.
Jesus, as He prays for the apostles and "those also who believe in [Jesus] through their Word" ("the entire number of the elect, all those who have been, who are, or who shall be gathered into one under Christ," 17:20). This prayer is not just for a bare confession, but for knowledge of God - theology:
- "...they have come to know that everything You have given Me is from You; for the words which You have Me I have given to them; and they received them and truly understood that I came forth from You, and they believed that You sent Me" (17:7,8). Jesus' giving of the Father's words to the disciples was considerably more than a presentation of "A.B.C." For Jesus, the foundation was to be built upon over an extended period of time - our whole lives from regeneration to the first death. Otherwise, why would the "Spirit of truth" (not the "Spirit of pragmatism") be promised to the Church?
- "Sanctify them in the truth; Your word is truth" (17:17). This is a prayer request for the Father - through the "Spirit of truth" by His Word, see 1 John 5:6 - to take the disciples beyond the initial bare confession of faith.
- "The glory which You have given Me I have given to them, that they may be one, just as We are one; I in them and You in Me, that they may perfected in unity, so that the world may know that You sent Me, and loved them, even as You have loved Me" (17:22,23). "Knowledge" is key to evangelism. What knowledge? The fullness of knowledge that the Father gave the Son and the Son taught to the disciples.
- "O righteous Father, although the world has not known You, yet I have known You; and these have known that You sent Me; and I have made Your name known to them, and will make it known; so that the love with which You loved Me may be in them, and I in them" (17:25,26). There's a lot of "knowing" going on here for us to just dismiss theology (the science of knowing God).
This is what Jesus, "the High Priest of our Confession" (Hebrews 3:1), prayed and continues to pray before the Father.