Please explain how OSAS and Matthew 7 verse 21 – 23 are different. Why do preachers use these verses to say if you are not living for the Lord and only the Lord knows your heart, then you may be headed for hell. And please help me understand how OSAS works, even for a Christian who is not living for the Lord.
First of all we have to understand that Matt. 7:21-23 is not about living for the Lord. Nor is it about OSAS. It’s about believing that His death paid the full price for our sins. (Also, from Matt. 7:15-20 we know it is directed toward false prophets, and therefore is not meant for general application.) We know these things because in Matt. 7:21 Jesus said that only those who do His Father’s will can enter the kingdom. John 6:38-40 tells us what His Father’s will is.
For I have come down from heaven not to do my will but to do the will of him who sent me. And this is the will of him who sent me, that I shall lose none of all that he has given me, but raise them up at the last day. For my Father’s will is that everyone who looks to the Son and believes in him shall have eternal life, and I will raise him up at the last day.”
The Father’s will is that everyone who looks to the Son and believes in Him will have eternal life. A few verses earlier Jesus said that’s all the Father requires of us (John 6:28-29). The same is true of John 3:16, Ephesians 2:8-9, Titus 3:4-7 and others. Trusting fully and exclusively in the Lord’s completed work on the cross is the only condition for salvation. Apart from that nothing will suffice, even the claim by those from Matt. 7:21-23 that they had done miraculous work in His name. The fact that He said He never knew them (Matt. 7:23) means they had never fully believed in Him in the first place and were depending upon their good works to finish the job they thought He had only begun.
OSAS works like this. Belief in Him is the only requirement for salvation, and once we believe our salvation is guaranteed (Ephesians 1:13-14). God Himself has set His seal of ownership on us and placed His Spirit in our hearts to make sure of this (2 Cor. 1:21-22). No one can ever take us out of His hands (John 10:27-30) and nothing can ever separate us from Him (Romans 8:38-39).
The Bible is abundantly clear in saying it’s what we believe that saves us, not how we behave. Our behavior is the way we demonstrate our gratitude for the free gift of salvation. It can do nothing to help us earn it or keep it.