I grew up hearing that one must be "saved", or to accept Jesus in their heart. Can anyone flesh this out and explain where this came from?
The concept of "saved" comes strait from the scriptures. Deborah13 quoted Ephesians 2:8 and the word "saved" occurs right in that verse. Of course there are many more verses that can be quoted in the scriptures with the word "saved" in it. Other terms in the NT that would related to the doctrine of salvation would be "gospel," "justified," "eternal life," and I am sure other terms could be included.
The concept of "accept Jesus into their heart" is a tradition that is only partially biblical. There is a lot of "heart" language in the NT, but nowhere in the scriptures will you see that we are to "accept Jesus into our heart." Typically, what other people do that believe in that tradition is to point to the "heart" language in the scriptures and assume that they only way the Spirit can get to the heart is by our invitation. I believe that the verse Eph 3:17 was quoted by Jethro Bodine above. He correctly stated that the Spirit dwells in the hearts of those saved, but that concept of the Spirit dwelling in the heart is not the same as "accept Jesus into their heart." The language is similar, but the concepts are very different.
I believe the "accept Jesus into your heart" tradition has a history in the preaching of one named "Charles Finney" (
http://en.wikipedia.org/wiki/Charles_Finney). Finney is considered the Father of American Evangelism. The theology of Finney leaned hard toward a low view of what Christ accomplished in the atonement or in his cross work. In the wiki link, you can read this statement....
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Finney's understanding of the atonement was that it satisfied "public justice" and that it opened up the way for God to pardon people of their sin."
Read the statement carefully. Notice how Finney takes a very low view of what Christ accomplished on the cross. Christs shed blood only "opened the way up for God to pardon people of their sin." In other words, Christ death saves no one, but only makes men savable. This leads to the question, what then saves them. In Finney's theology, salvation was gained by the decision you made. "Asking Jesus into your heart" would then be a decision by which you can fulfill the human requirements for God to pardon you. The basis of the pardon then is not the cross, but your decision. This began the tradition of "walking the sawdust trail." Of course this is a rejection of a biblical Christian understanding of salvation. It is a fairly recent invention. You will not find "accept Jesus into your heart" until Finney in the 1800s. Before that, the concept did not exist. To make a clear statement----> Finney was very unbibilcal.
Of course the scriptures speak of the gospel as "justification by faith." Now you might want to look up some older debates on this issue. The debate is about the human requirements for salvation. Is it faith alone, or faith and works. Other debates might be found about the nature of the word "justification" in the scriptures. To let you know where I stand, I believe in Justification by faith alone. Faith is the only human requirement, but it is also a gift from God through the work of the Holy Spirit in the New Birth (Phil 1:29; Eph 2:8; 1 John 5:1). This is also called "regeneration." So then, the heart is where the Holy Spirit works to change our nature with the result that we love and trust our Lord and Savior.
Salvation begins with an understanding of how sinful we are as the human race, and as individuals. Sin is far deeper than what is often admitted and realized. We do not merely do bad things, we are bad. We do not merely commit sins, we are sinners by nature. We offend God not merely by our bad deeds, but by who and what we are... sinners and rebels against a Holy God. You can make all the decisions for God that you want to, and you will continue in your sins. Salvation is by faith alone, through grace alone, by Christ alone.