The phrase spick and span means extremely neat and clean.

The adjective span new, meaning perfectly new, was derived from Old Norse spán-nýr, meaning literally chip new (cf. German Span, chip, shaving), the metaphor being as new as a freshly cut wooden chip as in the obsolete English adjective split new. The adjective span new is first attested in The lay of Havelock the Dane (circa 1285):

He ne hauede nouth to shride
But a kovel ful unride
Þat was ful and swiþe wicke
Was it nouth worth a fir sticke.
Þe cok bigan of him to rewe
And bouthe him cloþes al spannewe.
     in contemporary English:
He had nothing to wear
Except a rough cloak,
Which was so dirty and foul
That it was not worth a stick of firewood.
The cook came to feel sorry for him
And bought him brand new clothes.

The adjective spick and span new is an emphatic extension of span new. The first element, identical with spike in the sense of nail (German has the adjective nagelneu, meaning brand new, from Nagel, nail), seems to have been inspired by spik in the synonymous Dutch and Flemish expressions spikspeldernieuw, spiksplinternieuw and variants, meaning literally spike splinter new, the image being as new as a spike from the fire and a splinter from the block.

The obsolete French synonym of these expressions was tout battant neuf, literally wholly beating new (from the anvil). The usual expression is now flambant neuf, literally flaming new, the metaphor being (as in English brand new) as if fresh and glowing from the fire.

The expression spick and span new was first used by Thomas North (1535-1603?) in The Life of Paulus Aemilius, from The lives of the noble Grecians and Romanes (1579), the translation of the French rendering by Jacques Amyot (1513-93) of Parallel Lives by the Greek biographer and philosopher Plutarch (circa 46-circa 120):

The third squadron was of Macedonians, and all of them chosen men, as well for the flower of their youthe, as for the valliantnes of their persones : and they were all in goodly gilt armours, and braue purple cassocks apon them, spicke, and spanne newe.

A shortening of spick and span new, spick and span is first recorded in the diary of the English naval administrator Samuel Pepys (1633-1703):

(modernised spelling)
15^th November 1665—It was horrible foul weather; and my Lady Batten walking through the dirty lane with new spick and span white shoes, she dropped one of her galoshes in the dirt, where it stuck, and she forced to go home without one, at which she was horribly vexed.

Samuel Pepys was not saying that her shoes were clean or neat, but that they were brand new, which was the original meaning of spick and span. In A Dictionary of the English Language (1755), the English lexicographer Samuel Johnson (1709-84), defined the expression as meaning “quite new; now first used”. And, in Verses on the Death of Dr. Swift (1731), the Irish satirist, poet and Anglican cleric Jonathan Swift (1667-1745) made a bookseller say:

(1739 edition)
The Dean [= Swift] was famous in his Time;
And had a Kind of Knack at Rhyme:
His way of Writing now is past;
The Town hath got a better Taste:
I keep no antiquated Stuff;
But spick and span I have enough.