A sign is a devise in the Biblical narrative always set by God in order to affirm his authority, in order to increase the faith of man employed for a task at hand or as marker. Of the latter I shall take up first. Having set a rainbow in the sky God said,’..I do remember My Covenant which is between Me and You every living creature of all flesh.(Ge.9:12-17) This is different from the sign he employed to equip Gideon for his task. (Jud.6:36-40)
Here I want to focus on the office of the Holy Spirit in order to show a sign is employed as a starting point, which subsequently runs into many other agencies. Firstly let us read God’s covenant with Noah, ‘Noah, and with your seed after you… to every beast of the earth.’ Ge.9:8-10) The covenant with Noah enfolds all living things on the earth as well. In similar vein God’s promise to Abraham (Ge.12:1-3) covers not only Israel but all families. ‘In thee shall all families of the earth be blessed.(Ge.12.3, 28:14) God’s promises are universal and all inclusive and not limited to a few. As a sign of this divine nature we can understand the purpose of the lights from opening chapter of the Creation Account.
‘And God said, Let there be lights in the firmament of the heaven to divide the day from the night, and let them be for signs…(Ge.1:14).’ When Jesus announces ‘I am the light of the World..(Jn.8:12)’ we need to see he was a sign. ‘Therefore the Lord Himself shall give you a sign: Behold a virgin shall conceive and bear a Son, and shall call His name Immanuel(Is.7:14). Holy Spirit is Spirit of Truth. When God the Spirit states in the Creation Account light as a sign the redemptive nature of the Son of man is implied there.
In my book Marginalia- a concise guide to the Bible I have covered at length the manner God the Spirit has set the divine Will in signs, symbols and such like. Thus both standpoints of the God the Father and of the Son are clothed in a language which is Truth.