'Willingly' in the Bible

Then the chief of the fathers and princes of the tribes of Israel, and the captains of thousands and of hundreds, with the rulers of the king's work, offered willingly,

Then the people rejoiced, for that they offered willingly, because with perfect heart they offered willingly to the LORD: and David the king also rejoiced with great joy.

But who am I, and what is my people, that we should be able to offer so willingly after this sort? for all things come of thee, and of thine own have we given thee.

I know also, my God, that thou triest the heart, and hast pleasure in uprightness. As for me, in the uprightness of mine heart I have willingly offered all these things: and now have I seen with joy thy people, which are present here, to offer willingly unto thee.