Why would God want to deny us salvation?
Is He not love?
Is He not merciful and ready for forgive?
Did He not call us?
Did He not draw us?
Did He not enlighten us?
Did He not live the life we couldn't live ourselves and die the death we couldn't die for us, in our place?
Did He not determine the exact times and places that we should live so that we could seek Him and perhaps find Him even though He is not far from each of us?
Does He not command all men everywhere to repent?
Does He not work in us to will and to do according to His good pleasure? Does He not give us the Holy Spirit to lead and guide, strengthen and enlighten us?
Considering the lengths God has gone to to draw us to Himself and provide a means of salvation that anyone can have without cost, why on earth would we have any reason to NOT be sure of our salvation.
God WANTS to save us.
He's not looking for excuses to zap us as the *gotta work to earn our salvation* crowd would have us believe.
Rather everything Scripture teaches us that God is looking for excuses to SAVE us and not send us to hell.
Yet not all are saved. Do you really believe that all one has to do is say the magic words and then put it on autopilot? If you presume your Salvation you reject the gift of Hope.
He doesn't. Individual humans reject Him.