Since Jesus Came Into My Heart speaks of the change that takes place is us when we accept Jesus Christ as Lord and Savior and receive God's gift of salvation. The first verse of this hymn says:
What a wonderful change in my life has been wrought,
Since Jesus came into my heart;
I have light in my soul for which long I have sought,
Since Jesus came into my heart.
When we accept Christ and He is in our hearts, we are born again. We undergo a change. We become God's restoration project. 1 Corinthians 5:17 says that, when we are in Christ, we become a new creation. Our old corrupted self is gone, along with its deceitful desires, and it is replaced by a new self that starts to become more like Jesus. Our hearts and our minds are changed. Corruption is replaced by righteousness and holiness (Ephesians 4:22-24).
My wife and I live in a historic district of Plainfield, New Jersey. In this neighborhood, there are many old houses, some built in the 1800's. Oftentimes, when someone buys one of these old homes, they will look to restore it, making what is old and possibly a bit run down, look like new again. That is what God does with us when we accept His gracious gift of salvation through Christ. God begins to restore us.
When a home is being restored, the years of old paint covering its walls may be stripped away so that the walls can be covered with a fresh, new coat of paint. This is what happens with our hearts, souls, and minds when we are being restored by God. Our sins are stripped away, the old corruptible self is removed and we are then covered with the blood of the Lamb, Jesus Christ. Our sins, which were once scarlet, become as white as snow (Isaiah 1:18).
The process of restoring an old home can take a lot of time, months or maybe even years. The process of restoring our souls also takes time. When we receive salvation through Christ, the process of sanctification begins, as we are set apart for God's purposes. It is a process that continues throughout our lives as we are transformed into the likeness of Jesus (2 Corinthians 3:18). And, although this process will not be completed until Jesus returns, God promises that He will continue this good work He has begun in us until that day (Philippians 3:18).