'Stealthily' in the Bible

Being asked by the Pharisees when the Kingdom of God was coming, He answered, "The Kingdom of God does not so come that you can stealthily watch for it.

You who boast in the Law, do you [repeatedly] dishonor God by breaking the Law?

But [in those days] false prophets arose among the people, just as there will be false teachers among you, who will subtly introduce destructive heresies, even denying the Master who bought them, bringing swift destruction on themselves.

For certain people have crept in unnoticed [just as if they were sneaking in by a side door]. They are ungodly persons whose condemnation was predicted long ago, for they distort the grace of our God into decadence and immoral freedom [viewing it as an opportunity to do whatever they want], and deny and disown our only Master and Lord, Jesus Christ.