It is a reward for service to Christ. Matt.v. 11, l2. We are never said to be elect to the millennial kingdom. God means in this way to pay wages to His labourers, both of the Old Testament and of the New. It is given to sinners against their deserts.
Eternal life is the present possession of our calling.
The prize of our calling is to be sought for with effort. For the believer to be seeking after eternal life would be unbelief. For the believer not to be seeking after the prize of the Kingdom, is unbelief. Exhort one another daily, while it is called to-day, lest any of you be hardened through the deceitfulness of sin. For as human prizes require certain excellencies, and may be lost by the contrary offences, so with the prize of God.