How does it challenge God's sovereignty if we know we are of the elect? Our side would say that God wants us to know, and live in assurance. "If God is with us, then who can be against us?" (Rom. 8:31), and so forth. That strengthens our faith and helps empower us to obey (love) Him.
Amen. Either Christ died for our sins, or He didn't.
If Christ died for our sins, we are saved already because He has paid the price for our redemption. We stand acquitted before God and blameless because He took on the burden of our guilt and absolved us of it when He died in our place.
These things happened. They are real. Christ rose from the dead. He accomplished what He came to earth to do -- He redeemed His sheep, past, present and future.
"When God calls a sinner, He does not repent of it. God does not, as many friends do, love one day and hate another; or as princes, who make their subjects favorites and afterwards throw them into prison. This is the blessedness of a saint; his condition admits of no altercation. God's call is founded upon His decree, and His decree is immutable. Acts of grace cannot be reversed. God blots out His people's sins, but not their names." -- THOMAS WATSON
Read the Gospels, brother. Notice how the Pharisees act, those who "knew" they were saved. Read the letters of Paul. Notice how he attacks the Judaizers, those who "knew" they were saved.