There are several ways that the truth of the words of God has been declared.  The declaration of truth has been verbal, visible, written, and testified.

Verbal declaration – someone heard the Lord speak.  See Jn 1:18, 1 Jn 1:1-5, and 2 Pet 1:16-21.  At Mt Sinai, the Jew’s heard God speak directly from the mountain when he gave them the ten commandments, Ex 20.  They heard him speak; but we weren’t there to hear him speak these words to us.

Visible declaration – someone saw the Lord, Ezek 40:4, Rom 1:4.  In Ex 8:19 the magicians declared that “this is the finger of God” when he brought forth lice from the dust.  We didn’t see Ezekiel’s visions, and we didn’t see the Lord rise from the dead.  Yet, today, we can still see the invisible things of him through the visible things that he made, Ps 19:1-5, Ps 75:1, and Rom 1:20.  They declare his glory.

Written declaration – you can read what the Lord said, Lk 1:1-4, Prov 22:19-21.  And through these words you know the certainty of the things he said and the things you see.

Testified declaration – you can verify this declaration of truth by the testimony of others.  See Ps 96:1-4, Ps 119:13, Jer 31:10, and Acts 20:27.  We affirm (to state emphatically) the truth in our declaration of truth.

Conclusion: we weren’t there to hear God speak.  And we weren’t there to see him.  Nor were we given the privilege to write his words down.  But we have been given the responsibility and privilege to testify by our declaration of truth.