'Seal Up' in the Bible

it is He who has also put His seal on us [that is, He has appropriated us and certified us as His] and has given us the [Holy] Spirit in our hearts as a pledge [like a security deposit to guarantee the fulfillment of His promise of eternal life].

I protest, by the truth of Christ in me, that from this boasting no man shall seal up my lips in the regions of Achaia.