The truth of the gospel (and its’ related doctrines) MUST be simple … because God has declared that His people are primarily simple, poor, humble, repentant folks! None of God’s saving truths are revealed through intellect, education, reasoning, etc. because this would go against what God has said about His people. First, Jesus declares that we must be born again (from above, spiritually) … … if we are to see the kingdom of God, i.e. be part of His kingdom here and in heaven. God’s simple declaratives, such as John 3:16, simply say that … whoever believes in Jesus should not perish but have everlasting life. Let us assume that this is enough to cause the true believer to be born again, and most Christians think this means the Holy Spirit has entered the person: John 14:16-17 “He (Father God) will give you another (of the same kind) Helper, that He may abide with you forever — the Spirit of truth, whom the (unsaved) world cannot receive, because it neither sees Him nor knows Him; but you know Him, for He dwells with you and will be in you.” And this “Helper” teaches the believer (through the Spirit): John 14:26, John 16:13-14 “… the Holy Spirit, whom the Father will send in My name, He will teach you all things …” “… when He, the Spirit of truth, has come, He will guide you into all truth; for He will not speak on His own authority, but whatever He hears (from the Throne) He will speak … He will glorify Me, for He will take of what is Mine and declare it to you.” “Now if anyone does not have the Spirit of Christ, he is not His … But if the Spirit of Him who raised Jesus from the dead dwells in you, He who raised Christ from the dead will also give life to your mortal bodies through His Spirit who dwells in you.” (Romans 8:9-11) But, the KEY to everything is … “For as many as are being led by the Spirit of God, these are sons of God.” (Romans 8:14) Initially, God sanctified us (set us apart) … we were sealed (marked) as those who were going to be “worked on”, i.e. sanctified by the precious Holy Spirit. Yes, it’s a process, as in … “those who are being sanctified” (Hebrews 2:11 and 10:14) BUT … man has free will, and is fully able to reject this and refuse to co-operate! BUT … those who are sanctified successfully will inherit eternal life! Yes, those who are being led (i.e. those who are following) the precious Holy Spirit will be taught what it is that the Lord requires of them, such as: “Pursue holiness, without which no one will see the Lord” (Hebrews 12:14) “… as He who called you is holy, you also be holy in all your conduct, because it is written, “Be holy, for I am holy” ” (1 Peter 1:15-16) “… present your bodies a living sacrifice, holy, acceptable to God, which is your reasonable service” (Romans 12:1) “… to present you holy, and blameless, and above reproach in His sight, if indeed you continue in the faith, grounded and steadfast, and are not moved away from the hope of the gospel” (Colossians 1:22-23) “But now having been set free from sin, and having become slaves of God, you have your fruit to holiness, and the end, everlasting life” (Romans 6:22) “Therefore you shall be perfect, just as your Father in heaven is perfect” (Matthew 5:48) “… that He might present her to Himself a glorious church, not having spot or wrinkle or any such thing, but that she should be holy and without blemish” (Ephesians 5:27) “But let patience have its perfect work, that you may be perfect and complete” (James 1:4) There are literally dozens of warning verses written to the churches … warnings that they could lose eternal life … if they do wrong things instead of right things! But, IMO, the main purpose for us having the Holy Spirit … is so He can lead us through the sanctification process unto obedience, holiness, perfection, and eternal life! .