All the procuring of workmen and materials was over and the Ark was now complete, then God calls Noah and his family to come into the Ark to be saved. Christ has come and successfully undertaken all that was required of Him, so the invitation goes out to all to come to Him.
Having seen the deplorable behaviour of all mankind and revealing to Noah He was going to destroy man, the Lord God now reveals how this was going to happen yet save Noah and his family.