Strictly Grammatical Look is Not Enough
H3br3wHamm3r81's answer correctly points out the "οὐ μόνον ... ἀλλὰ καὶ" ("not only ... but also") wording in the verse, and correctly concludes "both" are granted.
But that does not entirely answer the question of its meaning, because one must ask in what sense the verse is saying such is granted.
There are at least two ways that it most naturally could be read:
Belief and Suffering Themselves are Granted
This would fall in line with a certain doctrinal view of soteriology in which faith itself is granted to people by God (not a decision one comes to, but rather a decision made for that one and given to them), and such is how one is saved. I will avoid the discussion of that doctrinal topic here, but simply note that is how the verse is read. If so, the parallel idea is that suffering itself is so granted also, and so every believer
(the one's here addressed, clearly seen in Phil 1:1, 5, 6, 25) will suffer since it is granted "on the behalf of Christ" (NKJV) or the "sake of Christ" (ESV).
For this parallel to hold, all believers must suffer (for Christ's sake) even as they were all granted faith. Leaving aside the arguments that occur between those that believe faith is so granted or not, this parallel creates a problem with respect to the suffering, because elsewhere in Scripture such suffering is noted as conditional upon "the desire to lively godly in Christ Jesus" (2 Tim 3:12), and for righteous behavior and reason for faith (1 Pet 3:13-17), and something commanded to be allowed for the testimony of Christ (2 Tim 1:8-12). In other words, suffering is not guaranteed to believers for merely being a believer, but rather only to those that live out that faith in a right manner of testimony for Christ. Death bed conversions (assuming such are a true conversion, and certainly some must be) would then violate that one must suffer for such a testimony.
These complications may lead one to consider the second possibility (if one might get past other theological thoughts that may hang them up from abandoning this first view)...
The Opportunity for Belief and Suffering are Granted
Much like if one were to get a phone call saying "You have been granted a trip to XXX [you name the place]," such a granting "to" something is an opportunity. It does not mean you will seize the opportunity to partake. In like manner, the wording in Philippians 1:29 "to believe" and "to suffer" may be deemed as opportunities. Certainly since the Philippian people Paul is addressing did believe, they had the opportunity to (noted in the gospel presentation mentioned in 1:5). They obviously seized that, and having that opportunity itself is for the sake of what Christ did (as the gospel proclaims).
So too, believers have an opportunity "for the sake of Christ" to suffer for Him. This suffering is conditional, but something Paul leading up to v.29 has been exhorting them to partake of. Note the contextual connections thus far:
- Paul's suffering in chains even now is to their benefit (v.7-8), and thus Christ's benefit.
- Paul's prayer for their love, righteousness, etc. (v.9-10); which, as noted above, if they engage in, they shall suffer for it.
- Paul's suffering benefited others to come to know Christ (v.12-13), and made bold other believers to speak of Christ (v.14).
- Paul even rejoices when Christ is preached for wrong reasons, reasons meant to increase Paul's sufferings (v.15-18)
- Paul rejoices in how such suffering, even if to death, magnifies Christ, because the suffering is from his testimony for Christ (v.19-21).
- Paul desires to suffer no more, to die and be with Christ, but yet is willing to continue to suffer for the testimony of Christ if need be, in part because it will benefit the Philippians for Paul to continue to live (v.22-24), and increase their faith by coming to them again (v.25-26).
- Paul thus exhorts the Philippians to behave right, have testimony of faith in the gospel, and not be fearful of what adversaries may do (v.27-28), that is, how they may suffer for those actions.
- Because Paul declares that such suffering for Christ is an opportunity they have before them to seize, for the sake of Christ Himself (v.29), and similar to Paul (v.30).
- And so suffer for the interests of Christ and of others (2:1-4).
I could go on further with the humility of Christ Himself, and such, but will end there in the analysis of Philippians, because I believe enough has been shown to merit (and further, recommend) this second view.
The second way of reading appears far stronger to me than the first. The context demonstrates that the granting "to suffer" is an opportunity that Paul is building a whole argument around in order to encourage the Philippians to seize it as their own opportunity to do something for Christ. It is a conditional action that he wants them to do.
And if the "to suffer" is so conditional, then the "to believe" (by parallelism) is also a conditional opportunity. Conditioned, at least in part, to the hearing of the gospel.