It is God... who has also put his seal upon us and given us his spirit in our hearts as a guarantee.
When you buy anything of value it nearly always comes with a guarantee. The maker's guarantee is his pledge that what you have bought works — if not it will be replaced.
When we come to faith in the Lord Jesus Christ we find that our salvation is a great work of God's grace and mercy. It is not something we have deserved — after all he only saves sinners! And when God saves us, this comes with a guarantee. Indeed he gives us a double guarantee. First of all he puts his seal on us — that declares that we belong to him. Then he gives us his pledge or guarantee that what he promises will truly be ours. God does this by giving us the Holy Spirit to live in our hearts to help us day by day to live in a Christian way and to keep us looking forward to the life in God's nearer presence when we die. That life will be the wonderful fullness or completion of what life here as a Christian will be like.
Now this should be of great comfort and encouragement to us when we are facing difficulties — perhaps physical pain or the sadness of a loved one's death. The grace and the love of God never changes. The hard times don't mean we don't belong to him any more or that he is not pleased with us. His seal and his guarantee remain. We are his for keeps!
Lord, help me always to keep in step with the Spirit you have given to me. Amen.