Simply because God sees the end from the beginning -- indeed from before the foundation of the world.But how could God claim them as His before they had made this decision?
Faith is NOT a work of righteousness, but simply trusting God and Christ, and believing the record that God has given regarding His Son and Christ's finished work of redemption. And Paul makes the distinction clear in Romans 4:And, if they are His because of their choice, how is that not works righteousness?
4 Now to him that worketh is the reward not reckoned of grace, but of debt.
5 But to him that worketh not, but believeth on him that justifieth the ungodly, his faith is counted for righteousness.
6 Even as David also describeth the blessedness of the man, unto whom God imputeth righteousness without works,...
16 Therefore it is of faith, that it might be by grace; to the end the promise might be sure to all the seed; not to that only which is of the law, but to that also which is of the faith of Abraham; who is the father of us all,...
23 Now it was not written for his sake alone, that it was imputed to him;
24 But for us also, to whom it shall be imputed, if we believe on him that raised up Jesus our Lord from the dead;
25 Who was delivered for our offences, and was raised again for our justification.
Also saving faith and genuine repentance are two sides of the same coin. And that should lead sinners to receiving Christ as both Lord and Savior.
ACTS 2
36 Therefore let all the house of Israel know assuredly, that God hath made that same Jesus, whom ye have crucified, both Lord and Christ.
37 Now when they heard this, they were pricked in their heart, and said unto Peter and to the rest of the apostles, Men and brethren, what shall we do?
38 Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost.