Jesus Christ had a clear answer to all who asked ,
Mat 19:16 And, behold, one came and said unto him, Good Master, what good thing shall I do, that I may have eternal life?
Well the answer to this question in truth is that one must do the Law and fullfill its righteous requirements. Well we know that the young man left Jesus Christ empty handed.
a couple from Germany--humanists but seriously seeking the truth and wanting to know God (if there is a God).
The Gospel of Jesus Christ is truth and its apologetics founded on truth.
Rom 3:10 As it is written, There is none righteous, no, not one:
Rom 3:11 There is none that understandeth, there is none that seeketh after God.
Rom 3:12 They are all gone out of the way, they are together become unprofitable; there is none that doeth good, no, not one.
Rom 3:13 Their throat [is] an open sepulchre; with their tongues they have used deceit; the poison of asps [is] under their lips:
Rom 3:14 Whose mouth [is] full of cursing and bitterness:
Rom 3:15 Their feet [are] swift to shed blood:
Rom 3:16 Destruction and misery [are] in their ways:
Rom 3:17 And the way of peace have they not known:
Rom 3:18 There is no fear of God before their eyes.
I dont know how this fits with your apologetics but Paul Speaking by the Holy Spirit was adamant that There are no human beings seriously seeking truth but rather all their throats are an open grave speaking lies. In my summation.
The evidence here is starkly clear, How is any humanist seeking God I want to inquire ?
Everything about and from a human being is evil completely. God is Righteous Holy and True Eternally. Nothing short of his Glory will do. Its an impossible task.
Is there a human of his own that ever did repent ?
Yes Truely a man must Repent. Turn away from evil 100%
How can it be we are sinners by nature wholey corrupt. But God demands Repentance !00% from a sincere heart. How can it be our hearts are totally evil, its impossible.
Mic 7:2 The good [man] is perished out of the earth: and [there is] none upright among men: they all lie in wait for blood; they hunt every man his brother with a net.
Mat 7:17 Even so every good tree bringeth forth good fruit; but a corrupt tree bringeth forth evil fruit.
Mat 7:18 A good tree cannot bring forth evil fruit, neither [can] a corrupt tree bring forth good fruit.
Mat 7:19 Every tree that bringeth not forth good fruit is hewn down, and cast into the fire.
Now if Jesus Christ who is God says that a corrupt tree cannot bring forth good fruit, How can the offspring of Adam who is a corrupt tree yeild good fruit humans.
Sing it with me " ITS IMPOSSIBLE"
Therefore the answer lies in the Gospel, good tidings how God himself took it upon himself flesh so as he is a Good fruit able to do and seek truth as a substitute for sinful humanity.
You see the Gospel must be preached on the foundation of truth. Once you have humans seeking truth then we dont need a saviour which is a lie.
What is impossible for a human is not with God.
So Jesus Christ is our substitution even in repentance. He acepted Baptism yet he was without sin to fullfill the Righteous demands of repenting which of ourselves we cannot do. Then He inhabits us by his Will and causes us to seek, pray, repent believe.
Salvation is of the Lord exclusively. We are receipients being made aware of the Truth, REVELATION. VESSELS OF HONOUR