The inner change is the complete focus of the Apostles.
:hammer:
Sorry, it's not. The central document of the NT is Romans about justification by faith. Justification is not an "inner" experience. Justification (as you may be able to tell just from the word itself) has to do with the day of God's judgement and with 'clearing' the individual believer for that. This does not and cannot be an inner experience. It is rather about what God the judge decides and declares.
"He to whom God wishes to speak, whether in anger or in love, cannot cease to exist."--Luther
Justification deals with the debt of sin; it does not deal with the stain or ongoing power. This is why Romans, Galatians, Colossians, Phillippians and several parables (the unforgiving manager; the disreputable woman at dinner) deal with debt. They do this by saying Christ's righteousness is credited/imputed/transferred to us. This does not happen "within" you; it happens in God's account or how he looks upon you. Of course, it changes your emotions enormously as an effect.
If the Gospel was an inner experience, there would be no need for the historic events of Christ. I had a friend in Bible college (no less) realize that he was so totally inward that he no longer believed there was any reason why Christ needed to come; it had no connection to anything in his mind and he gave up on it. God worked directly inside him; no need for the nonsense of the cross and the gore and blood and so forth.
There are two parts of salvation and they need proper relating:
1, Justification which God has done for us
in Christ
2, Inner change which God does
in us through the Spirit
#2 is not the Gospel. It cannot justify a person from their sins. It is a side effect of #1. The more excited you are about #1 the more motivated you are to 'work out your salvation in respect and trembling.' One is cause; the other is effect. We must not confuse cause and effect.