"When true Christians are, at any time, in the dark about their personal interest in Christ, they should as sinners, apply and trust the indefinite promises, directed in the gospel-offer to sinners as such; but, when they are assured of their interest in him, they may besides, apply and trust the definite promises, addressed to believers as such.
"The absolute promises, as they are directed in the offer to sinners indefinitely, are of general use (Hebrews 8:10-12). They serve as a ground of faith to such sinners, as are beginning to believe in Jesus Christ; and also to such believers, as are not assured by reflection, that they are already saints. Presented as they are, to sinners indefinitely, they are of course addressed, as a warrant for trusting in Jesus for salvation, to believers, considered in themselves as sinners. They are directed, not only to sinners without exception, who hear the gospel; but to saints, and that not as saints, but sinners in themselves and in their own view.
"The apostle Paul, long after his conversion, accounted himself the chief of sinners. In proportion as believers grow in grace, and in spiritual knowledge, the more sin, do they perceive in their hearts, and in all their thoughts, words, and actions. The less of remaining sin they have, the more of it do they see and feel. And sometimes, when their evidences of grace are veiled from their view, they can discern nothing in their hearts but sin; nothing in their past experience, but what appears counterfeit; and nothing in their present frame of mind, but strong, impetuous, and prevailing corruption. Now, the absolute promises are perfectly adapted to believers, when in such distressing cases. They are directed to sinners, and to believers as sinners; in order that they may warrantably apply, and trust, and plead them anew; or, that it may be warrantable for them, to come as sinners and trust them, as if this were but the beginning of their confidence. They are promises, not only of the first grace, but of all the future degrees of grace. Believers, therefore, have need to apply and trust them, at all time, and more especially, when they cannot discern their evidences of union with Christ. They are addressed in offer to them as sinners; that they may see their Divine warrant, for applying and pleading them, even in their deepest defection of spirit. When they can discern nothing in themselves, but sinfulness, then, they have the more need to look to, and fasten upon, the Lord Jesus in absolutely free promises. Whatever grace or degree of grace, they want, they are commanded, as sinners in themselves, to believe in the compassionate Saviour, and in believing, to take and trust those most comprehensive promises, as their security for it. —-
"On the other hand, when a believer is assured of his personal interest in Christ, he may then apply and trust the definite promises, which are addressed, in the gospel, to believers as such. Now that he is satisfied of his evidences of vital union with Christ, and so, of the reality of his union and communion with Him, he should embrace and trust, not only the indefinite, but the definite promises; in order that, he may be filled with all joy and peace in believing, and may abound in hope, through the power of the Holy Ghost."
John Colquhoun, A Collection of the Promises Of The Gospel; pp 17-20