Ephesians 1:
13 In whom [our Lord Jesus Christ] 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,
14 Which is the earnest of our inheritance until the redemption of the purchased possession, unto the praise of his glory.
According to Eph 1:13, we are sealed with that holy Spirit of promise.
And according to Eph 1:14, that holy Spirit of promise is the earnest of our inheritance.
The "earnest" (Gr. arrabōn) is a down payment, a pledge that the full amount will subsequently be paid.
See also:
2 Corinthians 1:21-22 Now he which stablisheth us with you in Christ, and hath anointed us, is God; Who hath also sealed us, and given the earnest (Gr. arrabōn) of the Spirit in our hearts.
2 Corinthians 5:5 Now he that hath wrought us for the selfsame thing is God, who also hath given unto us the earnest (Gr. arrabōn) of the Spirit.
The "seal" is the Holy Spirit of promise and in this lifetime the Holy Spirit of promise is given as a down payment (a portion) and it given as a pledge that the full amount will subsequently be paid. Knowing what I have received in this lifetime from God (which is such a blessing), I cannot imagine what our future in eternity holds for us.