Another tentative reader asked...
READER>> What harm is there in believing that God will save all mankind? Why would any object? Why is this good news even questioned? Your Biblical arguments seem clear enough.
ME>> Thank you for this question. You appear to be intellectually persuaded that the Bible teaches the salvation of all mankind. You also appear to be attracted to the prospects of the good news. Yet perhaps your reluctance and uncertainty is due to the traditions that surround you?
Some Christian traditions object, or even strongly object, because they do not think the Bible teaches that God's grace will be victorious in the salvation of all mankind. Furthermore, they may be concerned that this understanding could cause people to miss their understanding of the salvation message and thus be damned forever. These are important and noble concerns and so the hard work remains to properly understand the Bible and the gospel of grace. Repentance also is needed to confess that Jesus alone is the Savior.
I urge you to build your faith on the person of Jesus Christ and the Scriptures themselves rather than the tradition that makes you feel comfortable. Examine the Scriptures and pray, asking God to give you confidence in his truth.
As for my answer to your question, certainly I do not think there is any harm at all in believing that God will save all mankind through the grace of Christ! I believe this is the Biblical message and the good news of God's grace! However, I caution you to consider another question.
What harm is there in NOT believing that God will save all mankind?
If you join the Calvinists and believe that God does not love all mankind, but in fact only loves a sub-set of human beings, can any harm come from that way of thinking? Yes, in fact great harm! This is just the type of blind hypocrisy that Christ came to defeat through confronting the Pharisees. The Pharisees believed they were God's chosen people while disregarding God's love for the gentiles. Jesus reserved his strongest rebuke for these people! I do not think you want to hear Jesus rebuke you in the same way. That is not a safe place to stand.
If you join the Arminians and believe that God has merely offered his love, conditioned on each individual's choice, can any harm come from that way of thinking? Again yes, in fact great harm! Redefining God's unconditional love to be conditioned upon the 'choice of faith' undermines the invitation to trust that God has always loved you and your neighbor. Placing conditions on God's love perverts the Christian faith into just another pagan gentile religion of works. Jesus loved the Jews, the Greeks, and the Romans unconditionally, dying on the cross for all mankind. Trust in Jesus is confidence in his unconditional love. Trust is NOT a condition to his love! Please understand the difference. Christ was crucified once for all! Why crucify him again?
If you join those standing on the mystery in the middle of Arminianism and Calvinism, can any harm come from that way of thinking? Once again yes, in fact great harm! Mystery is hardly a safe place to stand for your own salvation or the salvation of your neighbor. Christ did not come to introduce confusion or mystery, but instead to reveal and explain the mystery of how our holy God could justify sinful man. The good and great news is that God the Son became a man, the second Adam, our vicarious substitute, to reconcile all mankind to God. The mystery is revealed in Christ. The Word of God promises confident knowledge of our salvation! Why obscure the good news with mysterious question marks?
Do you prefer the tradition that God does not love all? Do you prefer the tradition that God's love is conditional? Do you prefer mysterious question marks? The great harm of these understandings of "faith" is they fall short of Biblical hope in the Biblical Jesus. How can Jesus be pleased with this?
Look to Christ and his Word!