The redundancy is the invention of the KJV. A gift is only a gift if it is free, even Dr. E agrees with me on that one (miracle!). :) There is no NEED to specify it as 'free' as it would imply that there is such a thing as non-free gift. Verbosity comes to mind.
No, no oxymoron and no redundancy. :) I already gave you a modern day example of a conditional gift (man giving an engagement ring), but the concept was well known to the people of the time. For example, anyone knowing his scriptures was aware of the Mosaic Covenant. It was a conditional covenant. God promised to give the GIFT of His blessings in exchange for the obedience of the people. This was not an exchange of anything remotely resembling equal value so it has to be considered a conditional (non-free) gift.
God's saving grace was nothing like this at all. There were no strings attached, and no promise was required by men to receive saving grace. This makes "free" a useful adjective here.
If you say so, FK, useful maybe (for those who may doubt), but necessarily — definitely not.
God gave us life as well. We don't call it 'free gift (of life).' God gives us faith; we don't call it 'free gift (of faith).' Life an faith are something we actually have, grace is a pardon (unwarranted mercy) that we benefit from but don't have. It's not a state like freedom (which we don't call 'free gift' but an 'inalienable right').
Calling an engagement ring a 'gift' is also one of those 'oxymorons' because that act comes with conditional expectations. It's a 'deposit' a 'claim.' For some reason, man gives it to the woman and not the other way around, and women are not complaining. :)
A gift of a diamond ring would be a gift only if it were given to someone for no reason whatsoever. An engagement ring is a 'promissory item' usually but not always without a legal contract. It is given because someone wants something in return for it. It is therefore not a gift.