Hello Brad (and welcome to PB!),
I follow your blog, Heart & Mouth, and much appreciate it. Something that occurs to me with respect to the "substance" of what the faith of the OT saints cleaved to / stood upon: the
presence of God accompanying His word—in promises, types, depictions (cf Isa 53), etc—even as it is with us in the NT era. For us, when we are regenerated, it is usually on this wise:
...God, who commanded the light to shine out of darkness, hath shined in our hearts, to give the light of the knowledge of the glory of God in the face of Jesus Christ (2 Cor 4:6).
But it is always the case, whether in OT or NT times, and whatever the particular means God uses, that the Holy Spirit moves upon the heart of the elect to reveal God's presence, making the saint alive to Him, aware of Him, in love, and godly fear. In the OT we can see this in the dialogue between Moses and the LORD:
And Moses said unto the LORD, See, thou sayest unto me, Bring up this people: and thou hast not let me know whom thou wilt send with me. Yet thou hast said, I know thee by name, and thou hast also found grace in my sight. Now therefore, I pray thee, if I have found grace in thy sight, shew me now thy way, that I may know thee, that I may find grace in thy sight: and consider that this nation is thy people. And he said, My presence shall go with thee, and I will give thee rest. And he said unto him, If thy presence go not with me, carry us not up hence. For wherein shall it be known here that I and thy people have found grace in thy sight? is it not in that thou goest with us? so shall we be separated, I and thy people, from all the people that are upon the face of the earth. And the LORD said unto Moses, I will do this thing also that thou hast spoken: for thou hast found grace in my sight, and I know thee by name. (Exod 33:12-17) [emphasis added]
This is not merely Him dwelling in the visible pillars of cloud and fire (Exod 13:21), but His presence manifested to them, as it is written,
The LORD is nigh unto all them that call upon him,
to all that call upon him in truth (Ps 145:18)
Surely the righteous shall give thanks unto thy name:
the upright shall dwell in thy presence (Ps 140:13)
He enabled them to have a living, spiritual faith in Him, such as we see written of in Hebrews 11:1: "Now faith is the substance of things hoped for, the evidence of things not seen." Or, as Alexander Nisbet put it,
". . . it [is] the nature of true faith to make the thing it closes with spiritually present to the soul." –Alexander Nisbet, Commentary on 1st & 2nd Peter (Banner of Truth), p. 25.