To say that an unregenerate person can obey the Command of God to believe on the Lord Jesus Christ is a lie for Acts 16:31
30 And brought them out, and said, Sirs, what must I do to be saved?
31 And they said, Believe on the Lord Jesus Christ, and thou shalt be saved, and thy house.
Now understand, this believing is in regards to Salvation, to be saved, and the word believe here is pisteuó and its an:
Tense: Aorist
Mood: Imperative
Voice: Active
Imperative in the greek is defined as:
The imperative mood is a command or instruction given to the hearer, charging the hearer to carry out or perform a certain action.
Its a command here 1 Jn 3:23
23 And this is his commandment, That we should believe on the name of his Son Jesus Christ, and love one another, as he gave us commandment.
So this is to say in essence that an unregenerate person has the ability to Love God, for obeying God's Commands is an evidence of Love to God and His Christ Per Jn 14:15,21
15 If ye love me, keep my commandments.
21 He that hath my commandments, and keepeth them, he it is that loveth me: and he that loveth me shall be loved of my Father, and I will love him, and will manifest myself to him.
1 Jn 5:3
3 For this is the love of God, that we keep his commandments: and his commandments are not grievous.
And it is, we believe on Him only after the Spirit reveals God's Love to us by Giving His Son on our behalf Jn 3:16 ! So Our Believing is an act of response of our Love, for we Love Him because He First Loved us 1 Jn 4:19
19 We love him, because he first loved us. Our believing is under the influence of God's Love upon our regenerated hearts Rom 5:5, unless we say that an unregenerated heart, out of an principle of Law, obeyed the Commandment to believe on the Name of the Son of God !
Faith and Love go together in Jesus Christ, this is seen in Paul's conversion 1 Tim 1:13-14
13 Who was before a blasphemer, and a persecutor, and injurious: but I obtained mercy, because I did it ignorantly in unbelief.
14 And the grace of our Lord was exceeding abundant with faith and love which is in Christ Jesus.
Jn 16:27
For the Father himself loveth you, because ye have loved me, and have believed that I came out from God.
1 Pet 1:8
8 Whom having not seen, ye love; in whom, though now ye see him not, yet believing, ye rejoice with joy unspeakable and full of glory:
Faith and Love are both fruit of the Spirit Gal 5:22
22 But the fruit of the Spirit is love, joy, peace, longsuffering, gentleness, goodness, faith,
2 Cor 5:14-15
14 For the love of Christ constraineth us; because we thus judge, that if one died for all, then were all dead:
15 And that he died for all, that they which live should not henceforth live unto themselves, but unto him which died for them, and rose again.
The word constraineth is the greek word sunechó and means:
(a) I press together, close, (b) I press on every side, confine, (c) I hold fast, (d) I urge, impel, (e) pass: I am afflicted with (sickness).
This means that it , Love of Christ/ God is that which incites to action, imparts motion to !
Remember that Believing on Christ is an Imperative which means :
The imperative mood is a command or instruction given to the hearer, charging the hearer to carry out or perform a certain action.
We can perform this action without it being legalistic only as its a response to having our Hearts incited by the Love of God from Holy Spirit having poured it out in our hearts which is New Birth Rom 5:5
5 And hope maketh not ashamed; because the love of God is shed abroad in our hearts by the Holy Ghost which is given unto us.
Without this, the carnal heart is not subject to the Law / Command of God Rom 8:7-8
7 Because the carnal mind is enmity against God: for it is not subject to the law of God, neither indeed can be.
8 So then they that are in the flesh cannot please God.