Selfishness is not learned behavior—we are born with it. But when we accept Jesus as our Savior, He comes to live in our spirit, and as we learn how to “die to self” and follow the leading of the Holy Spirit, then we can overcome selfishness. It may never go away completely, but the Greater One who lives in us helps us overcome it daily (see Galatians 5:16).
Now, I haven’t overcome selfishness entirely, and I doubt anyone else has either. Even the apostle Paul, one of the greatest Christians who ever lived, had trouble overcoming selfishness. Learning to live unselfishly was a journey for him, just like everybody else. He said he had to "die to self" every single day.
We are called to the same life because we cannot live selfish lives and expect to make a difference. We must die to self every single day. It usually isn’t easy to do, but God will always give us His grace to do what’s right when we lean on Him. And the truth is, living an unselfish life is the best way to have more righteousness, peace and joy every day!
We do not need to strive for power or hope to have power someday; we have power now! The same power that raised Christ from the dead lives in us (see Rom. 8:11) and we can be quickened (filled with life) by that power. This is not a onetime filling that slowly drains out of us as the days go by, but we can be filled day by day and even moment by moment. We can constantly and continually experience God’s presence and power in our lives. When we belong to Him, there is never a time when His power is not accessible to us.