If God is not three in one, we cannot be saved...

Salvation is impossible with a non-trinitarian God.  Ephesians 1:3-14 is possibly the best explanation of this.  Each member of the Trinity is so interwoven in this text, it is difficult to separate them.  From the get go in verse 3, it says Blessed be the God and Father of our Lord Jesus Christ, who has blessed us in Christ with every spiritual blessing in the heavenly places.  According to this, it was the Father's work to bless us, but He did it in Christ.  We do not receive the Father's blessings apart from union with Christ.  From v. 13, we see that Holy Spirit seals these blessings for us; we are brought into union with Christ by the power of the Spirit (see also John 6:44).  

Another angle to view the Trinity's work in our salvation is to notice the progression in the passage.  Let me note that I learned this from "Pastor Joe" who is featured on this song that I highly recommend.  In verses 4 & 5, the Father chose us in [Christ] before the foundation of the world...In love, He predestined us for adoption as sons through Jesus Christ, according to the purpose of His will (notice again, the difficulty of separating this work from union with Christ).  From this we see that the Father arranged our salvation.  Then v. 7 says that in [Christ] we have redemption through His blood, the forgiveness of our trespasses.  Here we see that the Son, through His life, death, and resurrection, accomplished our salvation.  Finally, v. 13, [we] were sealed with the promised Holy Spirit.  The Holy Spirit applied our salvation.  

So why is salvation impossible without a Trinitarian God?  Because of His holiness and our sin.  In order for God to restore us to Himself, His justice and wrath must be satisfied.  So He arranged our salvation and sent His Son to accomplish it by dying a substitutionary death on the cross, bearing the guilt of our sin upon Himself and absorbing God's fierce and holy wrath.  He rose again proving that His death was victorious and now He commands all men to repent and believe this news.  However, men are still dead in their sin and are unable to come to Christ.  Therefore, the Holy Spirit comes and applies the work of Christ to our souls and gives us new hearts so that we can believe this Gospel when it is proclaimed.  And that Holy Spirit will continue applying that salvation so that we can persevere to the end.  

I pray this spurs us on to daily repentance and faith (especially those of you who have not received this message!).  May we be pleased to enter God's courts, through Christ, by the power of the Spirit, with thanksgiving and praise (Psa. 100:4)!