Sorry, that does not refer to unconditional love. It simply states nothing and no one can take away what belongs to God. And of course this doesn't refer to all mankind, but only those who are in Christ:
Ro 8:1 Hence, now there is no condemnation for those who are in Christ Jesus.
*That's a condition.
God has placed many conditions on us. Jesus took the punishment for our sin and reopened the gates to heaven, but it is solely up to us to accept that free gift or reject it.
If three of us are sitting at a table in my dining and I pour a cup of coffee for each of us, then set it in front of each of us, can you receive the coffee unless you physically reach out and take it? If you don't pick it up and drink, you will not get any coffee.
And so it is with salvation. It has been set in front of us, but we don't have to accept it.
*That's another condition.
and yet another condition:
Mark 16:16 Whoever believes and is baptized will be saved, but whoever does not believe will be condemned.