To be sealed is to be preserved and protected from contamination and destruction.
The Word and Holy Spirit catalyze to manifest authority and power.
→ no Word implies no authority
→ no Holy Spirit implies no power
→ Word + Holy Spirit manifests a Son Of God
When we are absorbed into Christ by being washed in the water of His Word and made righteous by His Holy Spirit our soul is sealed.
But this sealing only occurs if we trust only in the Word of the Lord and fellowship only with His Holy Spirit.
If there is a hole in that which seals, the effect of the seal is lost. Imagine a canned vegetable having a small hole in the rubber seal. The vegetable inside will rot.
So it is with the Seal Of God. There must not be a breach in our faith in the Word or our fellowship with the Holy Spirit.