It is one thing for the believer to dwell in God, but it is another thing for God to dwell in the believer. A believer can dwell in God and have all the safety and provisions of righteousness and all the coverings that he needs; but for God to dwell in a believer who still has a sin nature, it is quite another thing.
For the only way God can dwell in the believer is if He does away with all the wrong and wickedness about the believer. God is holy, righteous and perfect and because He is, He could not dwell in a believer if He still had to deal with the believer's original sin. But since He has done away with the penalty of sin and the imputation of sin in the character of His holiness, then a believer can have God dwell in him because of this atonement.
Man does not understand what it means to know Who God is, to dwell in Who God is, or to have Who God is dwell in him. Man thinks so often only of who he is instead of dealing just with Who God is. The result is that man enters into much self evaluation instead of thinking only in terms of God, thinking that would alleviate for man all kinds of problems.
Consider the provision. We are dwelling in God and that protects us forever from the devil, from the demons of Hell, and from all the enemies in the air. Also, God dwells in us protecting us from condemnation of sin and the habit and dominion of the sin nature; leaving the believer indwelt with righteousness imparted because of the atonement.