Contrariwise! That's exactly what the seal is, the earnest of our inheritance!
Ephesians 1:13 In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with that holy Spirit of promise,
Ephesians 1:14 Which is the earnest of our inheritance until the redemption of the purchased possession, unto the praise of his glory.
Sheep have to listen to his voice and follow Him. Those sheep nobody can snatch from Him.
We are not likened to sheep, but a new creature 2 Corinthians 5:17 KJV. It is Israel who are likened to that of sheep (Matthew 15:24 KJV)
Again, to whom Christ was sent Matthew 15:24 KJV. You can put your hand over your eyes and ignore it all you want, but it doesn't change the fact!